JOHN  ALEXANDER  JAMESON,  JR. 
1903-1934 


NGJNEERING  LIBRARY 


THIS  BOOK  belonged  to  John  Alexander  Jameson,  Jr.,  A.B.,  Wil- 
liams, 1925;  B.S.,  Massachusetts  Institute  of  Technology,  1928; 
M.S.,  California,  1933.  He  was  a  member  of  Phi  Beta  Kappa,  Tau 
Beta  Pi,  the  American  Society  of  Civil  Engineers,  and  the  Sigma 
Phi  Fraternity.  His  untimely  death  cut  short  a  promising  career. 
He  was  engaged,  as  Research  Assistant  in  Mechanical  Engineering, 
upon  the  design  and  construction  of  the  U.  S.  Tidal  Model  Labora- 
tory of  the  University  of  California. 

His  genial  nature  and  unostentatious  effectiveness  were  founded 
on  integrity,  loyalty,  and  devotion.  These  qualities,  recognized  by 
everyone,  make  his  life  a  continuing  beneficence.  Memory  of  him 
will  not  fail  among  those  who  knew  him. 


•vf 


GILBERT 

Hydraulic  and  Pneumatic 
Engineering 


BY 

CARLETON  JOHN  LYNDE,  Ph.D. 

PROFESSOR   OF   PHYSICS 
MACDONALD    COLLEGE,   QUE.,    CANADA 


Under   the   Direction   of 
ALFRED  C.  GILBERT 

Yale  University,    1909 

Illustrated  by  The  A.  C.  Gilbert  Art  Staff 

Published  by 
THE  A.  C.  GILBERT  COMPANY 

New  Haven,   Conn.,  U.   S.  A. 
New  York  Chicago  San  Francisco  London  Toronto 


INTRODUCTION 

NOWADAYS  there  are  so  many  very  interesting  things  going  on 
all  about  us  that  very  often  we  are  likely  to  overlook  things 
which  have  an  important  bearing  on  our  everyday  life.  Small 
things  which  we  are  so  used  to  having  around  that  we  never  stop  to 
think  what  they  really  mean  to  us. 

For  instance  water.  It's  nice  to  drink,  and  bathe  in  but  very  few 
of  us  ever  stop  to  consider  the  innumerable  uses  water  is  put  to  and 
what  a  great  influence  it  has  on  many  things  we  do.  Most  of  us  are 
satisfied  to  turn  on  the  faucet  and  get  our  water  in  that  way.  If 
something  is  wrong  and  the  water  doesn't  come  from  the  faucet  we 
call  up  the  plumber,  but  we  do  not  realize  what  has  gone  wrong  simply 
because  we  do  not  understand  how  a  house  is  piped  for  water  nor  do 
we  understand  why  water  gets  into  the  pipes,  etc. 

Then  air  —  another  thing  which  we  couldn't  live  without  and  yet  few 
appreciate  its  value.  Air  and  water  give  us  tremendous  results  as 
pneumatic  and  hydraulic  pressure.  A  knowledge  of  these  great  forces 
which  most  boys  are  so  familiar  with  and  still  do  not  understand  tho- 
roughly will  put  you  up  far  ahead  of  ,yyur,  fyby  friends.  Most  boys  take 
things  too  much  for  granted;  it  is  th.& -clever  boy  Who  digs  into  things 
and  find  out  the  reasons/  ' 

It  is  the  earnest  hope  of  the  authors  of  this  book  that  the  boys  who 
read  it  will  have  a  better  understanding  of  water  and  air,  how  they 
are  used,  and  what  they  mean  to  us. 

Sincerely  yours, 


COPYIUGHTEU,    1920,    BY    A.    C.     GlLBERr 

NEW  HAVEN,  CONN. 

ENGINEERING  LIBRARY 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING        3 
INDEX  TO  ILLUSTRATIONS 

HYDRAULIC  APPLIANCES 

City  Water  Supply Figs.  1,  2  —  Pages  5,  6 

Private  Water  Supply  Figs.  3,  4  —  Pages  7,  8 

Attic  Tank  System Figs.  7,  8  —  Page  10 

Water  Supply  From  Spring Figs.  11,  12  —  Page  12 

Pneumatic  Tank  Figs.  22,  23  —  Page  16 

Siphon  Over  Hill Figs.  31,  33,  35  —  Pages  21,  22 

Lift  Pump Figs.  62,  63  —  Page  43 

Force  Pump  Fig.  65  —  Page  45 

Hydraulic  Press  Figs.  68A,  73  —  Pages  48,  52 

Hydraulic  Elevator  Figs.  68B,  75  —  Pages  48,  53 

Hydraulic  Lift  Lock Figs.  68C,  79,  81,  82  —  Pages  48,  55,  58 

Depth  Bomb  Fig.  90  —  Page  66 

Torpedo  Figs.  91,  92  —  Page  67 

Submarine  Fig.  93  —  Page  68 

Battleship  Fig.  98  —  Page  72 

Raising  Sunken  Ships Figs.  105,  106,  108  —  Pages  79,  80,  81 

Floating  Dry  Docks  Figs.  109,  110  —  Pages  82,  83 

Air  Lock  in  Pipes  Figs.  120,  121  —  Pages  90,  91 

PNEUMATIC  APPLIANCES 

Magdeburg  Hemispheres  Fig.  122  —  Page  93 

Barometer  Figs.  129,  130  —  Page  99 

Air  Zones  Fig.  131  —  Page  100 

Altitude  Gauge Fig.  132  —  Page  101 

Air  Lift  Pump Figs.  139,  140  —  Pages  105,  106 

Balloons  Figs.  144,  145  —  Pages  110,  111 

Helium  Balloons  Fig.  146  —  Page  112 

Air  Brakes  Figs.  156,  157  —  Pages  121,  122 

Flame  Thrower Fig.  158  —  Page  123 

Fire  Extinguisher Fig.  160  —  Page  124 

Bicycle  Pumps  Fig.  165  —  Page  128 

Air  Compressor  Fig.  167  —  Page  130 

Sand  Blast  Fig.  168  —  Page  130 

Pneumatic  Paint  Brush Fig.  170  —  Page  132 

Diving  Bell Figs.  172,  173  —  Pages  133,  134 

Pneumatic  Caisson  Figs.  176,  177  —  Page  137 

Torpedo  Discharge  Tube Fig.  178  —  Page  138 

Air  From  Sea  Water Fig.  180  —  Page  140 


CHART  OF   HYDRAULIC  AND   PNEUMATIC   SEPARATE   PARTS 


ft  § 


No.  NAME  DESCRIPTION 

3300  TIN   TANK    7  7/8"  *  ?  ?f^  x  V^o"        i 

3301  BOTTLE    7  1/2"  High    Base,  2  1/2     x  1 

3302  GLASS  TUBE,   Long    5  1/2"  x  7/32"  diameter 

3303  GLASS  TUBE,   Short   2  3/4"  x  7/32 

IIS  8tttt  ^IlLILB6w-:::::::::::::::::  i  ift 

3306  GLASS  TUBE   TEE    3"  7/32^ 

3307  GLASS   TUBE   "U"    3"  7/32* 

3308  RUBBER    COUPLING    1  1/2"  x  1/4" 

3309  RUBBER   HOSE    16"         x  1/4" 

3310  RUBBER  STOPPER,  Laboratory  Style  No.  2  two  hole  3/16"  diameter 

3311  RUBBER  STOPPER,  Laboratory  Style  No.  1  Solid 

3312  RUBBER  STOPPER,  Laboratory  Style  No.  1  one  hole  I/JT  diameter 

3313  RUBBER  STOPPER,  Laboratory  Style  No.  0  two  hole   1/8 

3314  RUBBER  STOPPER,  Laboratory  Style  No.  0   one  hole  1/8 

3315  CLIPS,    Metal,   with   fastener    

3316  LARGE  GLASS  TUBE    1"  -80S"  diameter 

3317  WOOD    HANDLES     7"  ¥*J*rcd     ' 

3318  RUBBER    VALVES 1  1/2 "x  1/4' 

3319  GLASS  VALVES  NIPPLE    1"          x  7/32 

3320  BALLOON,    Dirigible  Type    

3321  BALLOON,    Observation   Type    .  lnlf 

3322  RUBBER  COUPLING,  Large  2 "          x  |/£ 

3323  RUBBER    BANDS     3  1/2"  x  1/8 

3324  RUBBER    BANDS     13/4 "x  l/}6 

3325  SHEET   RUBBER  PIECE    (White)    2"  x  11/2 

3326  SUBMARINE      1  3/4  < iiam.  d  am. 

1554  GLASS    FUNNEL    4  1/2"  long,  top  2^"       bot.   V* 

THE  A.  C.  GILBERT  CO.,  NEW  HAVEN,  CONN.,  U.S.A. 
In   Canada:    The  A.    C.    Gilbert  -  Menzks    Co.,   Limited,   Toronto,    Ontario. 


Hydraulic  and  Pneumatic  Engineering 

Hydraulic   Engineering   is    the  Engineering   which  deals   with  water  and 
other  liquids. 

Pneumatic    Engineering    is    the    Engineering    which    deals    with    air    and! 
other  gases. 


WATER  SUPPLY 

Boys,  have  you  running  water'irl  jy'eur  homes?.  ,,i|' so,  do  you  know 
how  it  gets  there?  You  will  shpw  how  with  this  .Engineering  set. 

If  you  live  in  a  city,  your  run^hig  w&i3r;is  "jEsuplpJi'eji  -'iih.  one  of  three 
ways:  first,  it  is  pumped  into  'a'stanclpipe  or 'reservoir;  second,  it  is 
brought  from  a  distant  lake  or  stream  at  a  higher  level;  or  third,  it  is 
pumped  directly  into  the  city  mains. 

The  standpipe  method  is  illustrated  in  Fig.  1.  The  water  is  pumped 
by  means  of  a  force  pump  B  from  a  river  or  lake  A  into  a  standpipe  C, 
from  which  it  runs  by  gravity  through  the  under-ground  pipes  or  mains 
to  the  houses  D,  fountains  E  and  hydrants  F.  This  system  is  used  in 
towns  and  small  cities  situated  in  a  flat  region,  because  it  is  the  cheap- 
est means  of  getting  the  water  above  the  level  of  the  highest  house 
faucet  in  the  town. 

If  the  town  is  situated  near  a  hill,  the  usual  practice  is  to  build  a 
large  cement  lined  reservoir  on  the  hill  and  to  pump  the  water  into  this 
instead  of  into  a  standpipe.  In  either  case  the  water  runs  by  gravity 
through  the  mains  and  submains  to  the  houses,  hydrants,  etc. 

If  the  city  is  very  large,  the  usual  practice  is  to  bring  the  water  from 
a  lake  or  stream  at  a  higher  level.  New  York  is  supplied  with  water 
in  this  way. 


Fl£f-  1.— (A)  Source  of  Water  Supply  (B)  Pumping  Station  (C)  Stand  Pipe  (D)  House 

Supplied  with  Water  (E)  Fountain   (F)   Hydrant  for  Fire  Hose. 
From  the  "Ontario  High  School  Physics",  By  Permission  of  the  Publishers 

See  page   145  for  diagram  of  apparatus  needed  to  perform  experi- 
ments  in  this  book. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


If  the  city  is  very  large  and  if  an  elevated  lake  or  stream  cannot  be 
found  within  a  reasonable  distance,  the  usual  practice  is  to  pump  the 
water  directly  into  the  city  mains,  from  the  nearest  river  or  lake. 

In  all  cases  the  greatest  care  is  taken  to  see  that  the  water  is  pure. 
The  land  bordering  the  elevated  lake  or  stream  is  kept  free  from  all 
sources  of  contamination  and  in  addition  the  water  is  filtered.  If  the 
water  is  pumped  from  a  lake,  the  intake  pipe  is  run  out  into  the  lake 
for  a  long  distance,  to  get  the  j>.urest«  water  and  in  addition  the  water  is 
filtered.  If  the  watej*.ls  pumpe<ij,fi|o5ai^a  river  near  the  city,  it  is  taken 
in  above  the  cijy^nd  is^  filtered. 


To  make  and  operate  a  city  water  supply  system  in 
which  the  water  comes  from  a  standpipe,  reservoir  or 
lake. 

Arrange  the  apparatus  as  shown  in  Fig.  2  and  bury 
the  mains  an  inch  or  two  in  sand  or  earth  if  convenient. 
Allow  the  water  to  run  from  the  house  faucet,  that  is, 
the  nozzle.  Attach  an  elbow,  hose,  and  nozzle  to  the 
hydrant,  that  is,  the  coupling,  and  allow  the  water  to  run. 

You  have  here  shown  how  the  water  runs  from  a 
standpipe,  reservoir,  or  elevated  lake,  through  the  mains 
to  the  hydrants  in  the  streets  of  a  city  and  to  the  faucets 
in  the  houses. 


Fig.  2. — Illustrating  a  City  Water  Supply  System. 

NOTE  1.  When  you  wish  to  insert  a  glass  tube  into  a  rubber  stopper 
or  coupling  always  place  the  stopper  or  coupling  in  a  glass  of  water 
to  wet  the  rubber  on  the  inside,  then  insert  the  glass  tubes  with  a 
twisting  motion.  Always  hold  the  glass  tube  near  the  end  you  are 
inserting  into  the  rubber  stopper  or  coupling.  Thi»  is  very  important, 
because,  if  you  hold  the  tube  too  far  back,  you  may  break  it. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING        7 

NOTE  2.    When  you  are  through  with  an  experiment  always  take  the 

apparatus  apart.     Be  sure  particularly   not  to  leave  a  glass  tube  in   a 

rubber   coupling   or   stopper  because    the    tube   will    stretch    the    rubber 

permanently  and  the  glass  and  rubber  will  stick  together. 

NOTE  3.    Make   the  experiments   out   of  doors,   in   the   garage,   in   the 

basement,  or  in  the  bathroom.    Keep  all  unused  tubes  in  the  box  where 

you  will  not  step  on  them. 

NOTE  4.     Let  Dad  enjoy  this  with  you;  he  was   a  boy  once,  and  will 

enjoy  the  fun   as  much  as  you   do. 

If  you  live  in  the  country,  or  in  a  town  wriere  there  is  no  public 
water  supply  system,  and  if  you  have  running  water  in  your  home, 
you  must  have  a  private  water  supply  system  of  some  kind, 

PRIVATE  WATER  SUPPLY 


Fig.  3.— A  Homestead  Supplied  with  Running  Water  by  Means  of  a  Windmill  and 
a  Storage  Tank  on  a  Tower. 

Courtesy  of  the  Stover  Manufacturing  Company 


8        HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


In  the  system  shown  in  Fig.  3  the  water  is 
pumped  by  means  of  a  windmill  and  force  pump 
into  a  tank  on  a  tower  and  from  this  it  runs 
by  gravity  to  the  house,  the  fountain,  and  the 
stable.  The  drawing  in  Fig.  4  shows  how  the 
water  from  the  tank  is 

•  distributed  to  the  laun- 
dry, kitchen,  and  bath- 
room of  the  house. 


Fig.  4. — Showing  How  Water  is  Distributed  in  the  House  to  the  Basement  Laundry, 
Kitchen  and  Bath  Room. 


EXPERIMENT  No.  2 

To  make  and  operate  a  private  water  supply  system  in  which  the 
water  is  stored  in  a  tank  on  a  tower. 

Arrange  the  apparatus  as  in  Fig.  5.  Hold  the  nozzles  horizontal 
and  open  them  one  at  a  time,  then  together.  Is  the  stream  from  the 
lower  nozzle  longer  than  that  from  the  upper? 

Arrange  the  apparatus  as  shown  in  Fig.  6.  Open  the  nozzles  when 
horizontal  and  at  the  same  level  Are  the  streams  of  equal  lengths? 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


You  have  shown  here 
how  the  water  runs 
from  a  tank  on  a  tow- 
er through  the  vertical 
pipe  and  underground 
pipe  to  the  faucets  in 
the  house.  You  have 
shown  also  that  the 
pressure  is  greater  at 
a  lower  faucet  than  at 
an  upper  faucet  and 
that  the  pressures  are 
equal  at  faucets  on  the 
same  level. 


^^^\'^j>^^;yy^ 


Fig.  6.— Showing     that     the     Water 

S~£','.  Pressures  are  Equal  at  Faucets  on  the 

*&*/ '« 

vf  £•   Same  Floor. 
sv'VC-V 


Fig.   5. — Showing    How    the    Water    Flows 
from  an   Elevated  Tank  to  the  Faucets. 


10     HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  7| — Water  Supplied  to  an  Attic  Tank  by  Means  of  a  Windmill  and  Pump 
Courtesy  of  the  Gould  Manufacturing  Company 

In  Fig.  7  the  water  is  pumped  by  a  wind- 
mill and  force  pump  into  a  tank  in  the 
attic  of  the  house,  and  from  there  it  runs 
by  gravity  to  the  various  house  fixtures  as 
shown  in  Fig.  8.  The  force  pump  is  often 
driven  by  a  gas  engine  instead  of  by  a 
windmill.  The  hand  pump  (4)  Fig.  8  is 
used  only  when  the  gas  engine  or  windmill 
is  out  of  order. 


Fig.  8. — Showing    How 
Water    is     Distributed    from 
an   Attic   Tank. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      11 


EXPERIMENT  No.  3 

To  make  and  operate  a  private  water  supply  system  in  which  the 
water  is  stored  in  an  attic  tank. 


Arrange  the  appara- 
tus as  in  Fig.  9.  Hold 
the  nozzles  horizontal 
one  above  the  other 
and  open  them  to- 
gether. Is  the  longer 
stream  from  the  lower 
nozzle?  That  is,  is  the 
greater  pressure  at  the 
lower  faucet? 


Fig.  9.— Showing  How 
Water  Flows  from  an 
Attic  Tank  to  Faucets 


Arrange  the  apparatus  as  in  Fig. 
10.  Hold  the  nozzles  horizontal  and 
open  them  together.  Are  the  streams 
of  the  same  length?  That  is,  are  the 
pressures  equal? 

You   have   shown   here 

again  that  the  greater 

pressure  is  at  the  low- 
er faucet  and  that  the 

pressures   are   equal  at 

faucets    on    the    same 

level. 


Fig.  10. — Showing  Again  that 
the  Water  Pressures  are  Equal 
at  Faucets  at  the  Same  Level. 


12      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


In  Fig.  11  the  water  from  an  ele- 
vated spring  runs  by  gravity  into 
a  storage  tank  and  then  through  an 
underground  pipe  to  the  house  fix- 
tures. 


EXPERIMENT    No.   4 

To  show  how  water 
is  brought  from  an 
elevated  lake  or  spring.  ' 

Arrange  the  apparatus  as  shown 
in  Fig.  12.  Place  the  tank  on  a 
mound  of  sand  or  earth  and  bury 
the  underground  pipe  to  a  depth 
of  one  or  two  inches.  Allow  the 
water  to  run. 


Fig.  11. — A  Home  Supplied  with  Water 
from  an  Elevated  Spring  and  Storage 
Tank. 


You  have  shown  here  how  the  water  is  brought 
to  a  city  from  an  elevated  lake  or  stream,  or  how 
it  is  brought  to  a  private  house  from  an  eleva- 
ted spring. 


Fig.  12.— Showing  How  Water  Flows  from  an  Elevated  Spring  to  the  Faucets 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      13 


a 


A  NAVAL  BATTLE 

GAME  No.  1 

You  can  invent  all  sorts  of  games  to  be  played  with  this 
Engineering  set.  The  Naval  Battle  is  one  and  it  is  an  excellent 
game  for  a  hot  day. 

Float  a  number  of  tin  cans,  tumblers,  or  cups  on  water  in 
a  bath  tub,  or  in  a  wash  tub,  Fig.  13.  Arrange  the  apparatus 
as  shown.  Each  player  directs  his  stream  against  the  warships 
of  the  other,  and  the  winner  is  the  one  who  first  sinks  all  the 
enemy  war  ships. 

PNEUMATIC  TANK  SYSTEM  OF  WATER  SUPPLY 

The  pneumatic  tank  system  of  water  supply  is  illustrated 
in  Fig.  14.  The  water  is  pumped  into  the  bottom  of  an  air- 
tight steel  tank  and  compresses 
the  air  in  the  tank  to  smaller  vol- 
ume  at  the  top.  This  compressed 
air  then  forces  the  water  out 


Fig.  13.— A  Naval  Battle, 
through  the  discharge  pipe  at  the 
bottom  of  the  tank  and  lifts  it  to 
the  faucets  in  the  rooms  above. 
The  interior  of  the  tank  is  repre- 
sented in  Fig.  15.  The  compressed 
air  at  the  top  of  the  tank  forces 
water  up  the  discharge  pipe  when 
any  faucet  C  is  opened. 


DISCHARGE 
PIPE    — 


COM- 
PRESSED 
AIR 


CHECK 
VALVE 


Fig.   14.— A  House  Supplied  with  Water 
by  Means  of  a   Pneumatic  Tank. 
Courtesy   of  The  Andrews  Heating  Co, 


Fig.  15. — Showing    How   the    Air 
is  Compressed  in  a  Pneumatic  Tank. 
Courtesy  of  the  MacMillan  Co. 


14      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


EXPERIMENT  No.  5 

To  make  and  operate  a  pneumatic  tank. 

Arrange  the  apparatus  as  shown  in  Fig.  16. 
It  is  necessary  to  fasten  the  stopper  in  the  bottle  very  securely. 
Do   this   as   follows :   Insert   two   elbows    into   the   two-hole 
rubber  stopper  and  twist  the  stopper  firmly  into  the  neck 
of  the  bottle.    Next  loop  three  strong  rubber  bands  to- 
gether  as    shown    in    Fig.    17,   pass    a    stout    cord   over 
the  stopper  and  wind  the  stretched  rubber  bands  a- 
round  the  neck  and  cord.    Now  slip  the  last  end  of 
the  bands   under   the  last  winding  to   hold   it,    (1) 
Fig.  18,  then  tie  the  ends  of  the  cord  up  over  the 
stopper,   (2)   Fig.  18,  and  you  will  find  that  the 
stopper  is  very  secure. 


Fig.  16.— Operating 
a   Pneumatic  Tank. 


Fig.  17. 

The  stretched  rubber  bands  make 
a  very  secure  tie  because  each 
Stretched  winding  grips  the  cord. 
You  will  use  this  tie  often  in  your 
experiments. 

Note — You    can   use   the    tee   and 

one-hole  stopper  instead  of  the 
elbows  and  two-hole  stopper  if 
you  prefer. 


Fig.  18. — Showing  How  to  Make  a 
Stopper  Secure  by  Means  of  Cord  and 
Looped  Rubber  Bands. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      15 


Now:  open  the  clip  on  the  hose,  open  the  faucet 
Fig.  16,  slightly,  run  water  into  the  bottle  until  it  is 
half  full,  close  the  faucet,  close  the  clip  on  the  hose, 
remove  stopper  from  faucet,  point  the  nozzle  upward, 
and  open  the  clip  on  the  nozzle. 

Does  the  compressed  air  force  the  wa- 
ter out  with  surprising  force? 
If  you  have  no  water  faucet  handy,  illus- 
trate the  pneumatic  tank  as  shown  in  Fig. 
19.  Fill  the  bottle  half  full  of  water,  tie 
the  stopper  in  place,  force  air  in  with  your 
mouth  or  with  a  bicycle  pump,  and  observe 
the  stream  as  before. 


Fig.  19. — Operating    a     Pneu- 
matic  Tank  in  Another  Way. 


Fig.  20. 


Fig.  21. 


Find  a  larger  bottle,  which  your  stoppers  will  fit,  and  repeat  these 
experiments. 

You  have  shown  here  how  the  compressed  air  in  a  pneumatic  tank 
forces  the  water  out  through  the  discharge  pipe.  Repeat  and  make 
experiments  of  your  own. 

Note— Do  not  attempt  to  fill  the  bottle  more  than  half  full  of  water 
because  the  air  pressure  increases  rapidly  as  the  air  is  compressed  and 
it  blows  out  the  nozzle  or  separates  the  rubber  tubes  from  the  elbows. 


16      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


RAPID  FIRE  WATER  GUN 
GAME  No.  2 

Arrange  the  bottle  as  shown  in  Fig.  21  and  fill  it  half  full  of  water. 
Replace  the  elbow  by  a  nozzle  as  in  Fig.  20  and  your  rapid  fire  water 
gun  is  complete.  Open  the  clip  for  an  instant  only  for  each  shot. 

Arrange  a  battle  with  one  or  more  on  a  side,  each  soldier  armed 
with  a  rapid  fire  water  gun.  A  man  is  wounded  when  hit  on  the  arm 
or  leg  and  must  afterwards  fight  without  the  arm  or  leg;  a  man  is 
killed  when  hit  on  the  body  or  head.  The  side  loses  which  first  has  all 
of  its  men  killed.  Use  forts,  trenches,  tanks,  etc. 


EXPERIMENT  No.  6 


To  make  and  operate  a  pneumatic  tank  system  of  water  supply. 

Arrange  the  apparatus  as  in  Fig.  22,  fill  the  bottle  half  full  of  water 
as  above,  open  the  clip  on  the  discharge  tube,  and  observe  the  height 
to  which  the  compressed  air  lifts  the 
water. 

Repeat   with    the    apparatus    as    in 
Fig.    23.    Do    you    observe    that    the 
stream  from  the  lower  nozzle  is  long- 
er than  that  from  the  upper;  that  is, 
that    in    the    pneumatic    system    also 
the     pressure     is     always 
greater  at  the  lower  fau- 
cet? 


Fig.  23. — Water    Pressure    is    Greater    at    the 
Lower  Faucet. 


Fig.  22. — The  Compressed  Air 
in  a  Pneumatic  Tank  Forces 
Water  Up  the  Discharge  Pipe. 

A  — 1 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      17 


Repeat  with  the  apparatus  as  in  Fig.  24.  Do  you  observe  that  the 
streams  are  of  the  same  lengths,  that  is,  that  the  pressures  are  equal 
at  faucets  on  the  same  level? 

You  have  shown  here 
how  the  compressed  air  in 
a  pneumatic  tank  forces 
water  up  to  the  faucets 
above ;  also  that  the 
greater  pressure  is  at  the 
lower  faucet,  and  that  the 
pressures  are  equal  at 
faucets  on  the  same  level. 


Fig.  24.— The  Water  Pressures  are  Equal. 


A  — 2 


18      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


WATER  AND  AIR 

EXPERIMENT  No.  7 

To  show  that  water  is  incompressible  and  that 
air  is  compressible. 

Arrange  the  apparatus  as  in  Fig.  25,  fill  the 
tube  with  water  and  try  to  compress  it.  You 
cannot  do  so  because  water  is  nearly  incom- 
pressible. 

Note:  Water  as  slightly  compressed  by  very 
great  pressures;  for  example,  if  your  tube  were 
10  in.  long  and  you  could  apply  a  pressure  of 
3000  Ibs.  per  square  inch,  the  water  would  be 
compressed  1/10  inch. 

Now  empty  out  the  water  and  try  to  compress 
the  air  in  the  tube  as  in  (2)  Fig.  25.  You  will 
find  that  you  can  do  so  quite  easily  because  air 
is  quite  compressible. 

You    have    demonstrated    here    that    water    is 
incompressible  (nearly)  and  that  air  is  compress- 
ible.   You  know  from  this  that  in  the  pneumatic 
tank  it  is  the  air  which  is  com-         ^\ 
f±      pressed  and  not  the  water.    XJ 


1  2 

Fig.  25. — Showing 
that    water    is   in- 
compressible and 
that  air  is  com- 
pressible. 


1 

Fig.  26. — Corn- 


pressure. 


EXPERIMENT  No.  8 

To  show  that  compressed  air 
exerts  pressure. 

Use  the  apparatus  shown  in  Fig. 
26.    Wet  the  inside  of  the  tube,  wet 
the  plunger  and  rub  it  on  a  cake  of 
soap    to   make    it    slippery,    shove    the 
plunger  into  the  tube  (1)  and  let  it  go 
suddenly. 

Do    you    find    that    the    compressed    air 
drives  the  plunger  out  violently  (2)? 

Repeat  with  a  little  water  above  the  plunger 
to  serve  as  a  lubricant. 

Note:  When  you  shove  the  handle  into  the  stoP~ 
per  you  expand  the  stopper  slightly.    You  should 
expand  it  until  it  fits  the  tube  snugly  but  not  too 

1  Hold  the  apparatus  as  in  (3),  Fig.  26  and  force  the 
handle  in  until  the  compressed  air  drives  out   the  end 
stopper. 

You  have  shown  here  that  compressed  air  exerts  pres- 
sure and  you  will  understand  from  this  how  the  com- 
pressed air  drives  the  water  out  of  a  pneumatic  tank; 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      19 


also  you  will  understand  why  the  tank  must  be  made  of  steel,  namely, 
to  stand  the  pressure  of  the  compressed  air. 

TRENCH  GUN 

GAME  No.  3 


Fig.  27.— Trench    Gun. 


You  can  imitate  the  Stokes  trench  gun  as  follows.  Put  two  long 
strips  of  paper  on  the  ground  three  feet  apart  to  represent  the  enemy 
trench.  Now  go  back  20  or  30  feet  or  more,  point  the  tube  upward  and 
toward  the  enemy  trench,  force  the  plunger  in  and  release  it  suddenly. 
The  game  is  to  try  to  drop  the  bomb,  that  is,  the  plunger,  into  the 
enemy  trench.  The  winner  is  the  one  who  does  it  most  often  in  a  given 
number  of  trials. 

Note:  Keep  the  inside  of  the  tube  wet,  the  plunger  wet  and  slippery 
with  soap,  and  a  little  water  above  the  plunger. 

HEIGHT  AND  DISTANCE  CONTEST 

GAME  No.  4 

Use  the  apparatus  as  above.  The  game  is  to  see  who  can  shoot 
the  plunger  to  the  greatest  height  and  to  the  greatest  distance. 

POP  GUN 

GAME  NO.  5 


Fig.  28.— Pop  Gun. 

Use  the  apparatus  as  a  pop  gun,  Fig.  28.  The  games  are:  first,  to 
try  to  hit  a  bull's  eye,  with  the  end  stopper;  second,  to  see  which  can 
shoot  it  to  the  greatest  distance  and  the  greatest  height. 


20       HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  29.— A  Siphon. 
Courtesy  of  The  MacMillan  Co. 


THE  SIPHON 

The  siphon  is  used  in  many  wa- 
ter supply  systems  to  make  water 
flow  over  the  top  of  a  storage 
tank  or  over  a  hill  from  a  spring 
on  one  side  to  a  house  on  the 
other,  and  so  on. 

You  will  first  show  how  the  si- 
phon works,  then  you  will  show 
how  it  is  used  in  water  supply 
system,  and  later  you  will  show 
why  it  works  as  it  does. 


EXPERIMENT  No.  9 

To  make  and  operate  a  siphon. 


Arrange  the  apparatus 
as  in  (1),  Fig.  30.  Place 
one  arm  of  the  siphon  in 
the  water  and  while  hold- 
ing the  other  arm  outside 
the  tank  below  the  water 
level  suck  the  air  out  of 
the  siphon  until  the  water 
runs. 

Does  the  water  run  up 
hill  to  the  top  of  the  si- 
phon and  then  down  hill 
into  the  tumbler? 

Siphon  water  out  of  a 
full  tumbler  into  an  empty 
tumbler  and  while  the  wa- 
ter is  running  stand  them 
side  by  side  on  the  table, 
(2),  Fig.  30. 

Does  the  water  stop 
when  the  level  is  the  same 
in  both  tumblers? 


(3)  (4) 

Fig.  30. — Illustrating  the  Siphon. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      21 


Place  one  tumbler  on  a  block  of  wood  or  a  book  as  in  (3),  Fig.  30. 

Does  the  water  flow  from  the  upper  tumbler  to  the  lower,  and  does 
the  flow  again  stop  when  the  levels  are  the  same? 

Place  the  block  under  the  other  tumbler. 

Are  the  results  the  same? 

Repeat  the  above  experiments  with  the  rubber  hose,  (4),  Fig.  30,  used 
as  a  siphon. 

You  have  shown  here :  that  the  water  runs  uphill  in  one  arm  of  a 
siphon  and  downhill  in  the  other;  that  it  always  runs  from  the  higher 
water  level  to  the  lower;  and  that  it  stops  running  when  the  water 
levels  are  the  same. 

You  will  show  "why"  the  water  runs,  in  later  experiments. 


HOW  THE  SIPHON  IS  USED  IN  WATER  SUPPLY  SYSTEMS 

EXPERIMENT  No.  10 

To  show  how  the  siphon  is  used  in  water  supply 
systems. 

It  is  rather  difficult  to  make  a  water-tight  con- 
nection in  the  bottom  of  a  water  tank  and  in  many 
cases  it  is  not  done,  but  instead  the  water  is  si- 
phoned out  over  the  top,  as  shown  in  Fig.  31. 

Illustrate  this  as  shown  in  Fig,  32. 


Fig.  32.— Showing 
How  Water  is  Siph- 
oned Out  of  an  Ele- 
vated Tank. 


Fig.  31.— The  Arrangement  of  Piping  Used  to  Siphon 
Water  Over  the  Top  of  a  Storage  Tank. 


22      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


In  some  cases  it  happens  that 
there  is  a  good  spring  of  water 
on  one  side  of  a  hill  and  the  home 
in  which  the  water  is  wanted  is  on 
the  other  side.  If  the  highest  point 


Fig.  33. — The  Arrangement  of  Piping 
Used  to  Siphon  Water   Over  a  Hill. 


of  the  siphon  is  not  more  than  about  25  feet 
(34  feet  is  the  theoretical  limit)  above  the 
water  surface  in  the  spring,  and  if  the  house 
faucets  are  below  the  level  of  the  water  in  the 
spring,  the  water  can  be  siphoned  over  the 
hill  as  shown  in  Fig.  33. 

Illustrate   this   as   shown   in  Fig.  34,  where 
the  back  of  the  chair  represents  the  hill. 


Fig.  34. — Showing  How 
Water  is  Siphoned  Over 
a  Hill. 


Fig.  35.— The  Arrangement  of  Piping  Used  to  Siphon 
Water  Over  a  Hill  from  a  Storage  Tank. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      23 


Water  can  be  siphoned  from  a  storage  tank  or 
reservoir  over  a  hill  as  well  as  from  a  spring  and 
the  siphon  can  start  at  the  bottom  of  the  reservoir 
if  this  is  more  convenient,  see  Fig.  35. 

Illustrate  this  as  shown  in  Fig.  36. 

You  have  here  illustrated  three  ways  in  which  the 
siphon  is  used  in  water  supply  systems.  You  will 
show  later  why  a  siphon  cannot  lift  water  over  a 
rise  of  more  than  about  25  feet  and  why  the  greatest 
theoretical  lift  is  34  feet. 

HOW  TO  START  A  LARGE  SIPHON 


EXPERIMENT  No.  11 


Fig.  36. — Siphoning 
Water  Over  a  Hill  from 
a  Tank. 


To   illustrate   different   ways   of 
siphon. 

You  could  not  start  a  large  siphon  by  sucking 
the  air  out  of  it  with  your  mouth.  How  then  are 
you  going  to  start  it?  You  will  illustrate  three  ways. 
The  object  in  all  cases  is  to  get  the  air  out  of  the 
siphon  and  this  is  usually  done  by  filling  it  with 
water. 

In  the  case  illustrated  in  Fig.  37,  the  faucets  are 
all  closed  and  the  air  is  driven  out  of  the  siphon  by 
pumping  water  into  the  tank  through  the  siphon. 
The  check  valve  prevents 
the  water  from  running 
back  into  the  pump,  and 
when  the  faucets  are 
opened  the  water  runs. 


starting  a   large 


V. a  •'.:-•-•  <f.Sw!R« 


Fig.  37.— The  Large  Siphon  is  Started  by  Pumping 
Water  into  the  Tank  through  the  Siphon. 


24      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


This  experiment  is  illustrated  by  means 
of  the  apparatus  shown  in  Fig.  38.  The 
faucet  here  represents  the  pump.  Start 
with  the  tube  empty  except  for  the  air  in 
it,  close  the  clip  under  the  nozzle,  open  the 
faucet  until  the  tank  is  full  of  water,  close 
the  faucet,  and  open  the  clip. 

Does  the  water  run  through  the  siphon 
to  the  nozzle? 


When  the  water  is  siphoned  over  a  hill 
from  a  spring,  the  siphon  is  usually  started 
by  connecting  it  to  the  suction  side  of  a 
pump  placed  on  the  other  side  of  the  hill 
in  or  near  the  house,  as  shown  in  Fig.  39. 


Fig.  38. — Illustrating  One 
Method   of   Starting   a   Large 
Siphon. 


Fig.  39. — The  Large  Siphon 
is  Started  by  Pumping  Water 
Out  of  the  Spring  through  the 
Siphon. 


To  start  the  siphon,  the  house  fau- 
cets are  closed,  the  stop  cock  at  the 
pump    is    opened    and    the    pump    is 
operated  until  the  water  comes   freely;   then 
the   stop   cock   is   closed   and   the  water  runs 
whenever  a  faucet  in  the  house  is  opened. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      25 


This  is  illustrated  by  arranging  the  apparatus  as 
shown  in  Fig.  40;  the  tee  branch  represents  the  pump 
connection  and  the  end  branch  represents  the  house 
pipe. 

Close  the  house  pipe,  apply  your  lips  to  the  tee 
branch  (to  represent  the  working  of  the  pump)  and 
suck  air  out  of  the  siphon  until  the  water  flows,  then 
close  the  tee  branch  and  open  the  house  pipe.  Does 
the  water  flow? 


Fig.  40. — Starting  a  Large  Siphon. 


In  many  cases  the  water  is  siphoned  over 
the  top  of  a  hillside  well  to  a  house  at 
a  lower  level  and  the  siphon  is  started  by 
means  of  a  pump  near  the  house  as  illus- 
trated in  the  last  experiment.  Generally, 
however,  a  small  storage  tank  of  water  at 
the  top  of  the  siphon  is  used  to  start  it, 
see  Fig.  41.  The  small  storage  tank  is 
filled  by  means  of  a  pump  (not  shown),  or 
by  means  of  a  pail  used  to  dip  water  from 
the  well. 


Fig.  41. — A  Large  Siphon  is 
Started  by  Allowing  the  Water  to 
Flow  Through  It  from  the  Small 
Storage  Tank. 


26      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Illustrate  this  method  of  starting  a  large  siphon 
with  the  apparatus  shown  in  Fig.  42.  The  tee  at  the 
top  is  connected  with  the  metal  tank,  which  here 
represents  the  small  storage  tank,  the  large  pail 
represents  the  hillside  well,  and  the  long  arm  of 
the  siphon  represents  the  pipe  to  the  house. 

Open  the  house  faucet,  then  open  the  tee 
connection  to  the  storage  tank.  Does  the 
water  flow  down  the  long  arm  of  the  si- 
phon? Now  close  the  house  faucet  and 
observe  that  the  wfeter  runs  down  the 
short  branch  into  the  pail.  Now  close  the 
tee  connection  and  open  the  house  faucet. 
Does  the  siphon  run? 


Note:  The  storage  tank  needs  to  be  filled 
only  when  the  siphon  stops,  which  may  be 
only  once  or  twice  a  year. 


Fig.  42.— Showing    How   a 
Large    Siphon    is    Started    by 
Means  of  Water  from  a  Small 
Storage  Tank. 


OTHER  USES  OF  THE  SIPHON 

EXPERIMENT  No.  12 

To  illustrate  other  uses  of  the  siphon. 

You  can  siphon  cider,  or  other  liquids,  out  of  a  barrel  by  means  of 
a  rubber  tube,  (1)  Fig.  43. 

Illustrate  this  as  in  (2)  Fig  43,  where  the  bottle  represents  the  barrel 
and  the  neck  of  the  bottle  the  bung  hole. 


Fig.  43. — Siphoning  Cider 
Out  of  a  Barrel. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      27 


--Hi 


Fig.  44.— Siphoning  Water  Out  of  a  Boat. 

You  can  siphon  water  out  of  your  boat  when 
it  is  out  of  the  water,  (1)  Fig.  44,  but  not  when 
it  is  afloat. 

Use  a  tumbler  to  represent  your  boat  and 
show  that  you  can  siphon  water  out  of  it 
when  it  is  out  of  the  water,  (2)  Fig.  44; 


but  that  you  siphon  water  into  the  boat  if 
it  is  afloat,  (3)  Fig.  44,  because  the  water 
outside  the  boat  is  higher  than  that  inside. 

You  can  siphon  sand,  gravel,  and  mud  with 
the  water  when  necessary.  Illustrate  this  by 
siphoning  sand  or  mud  with  the  water  from 
one  tumbler  to  another,  Fig.  45, 


Fig.  45.— Siphoning  Sand. 


28      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


VELOCITY  OF  FLOW 

EXPERIMENT  No.  13 

To  show  that  the  velo- 
city of  the  water  in  a  si- 
phon is  greater,  the  great- 
er the  distance,  between 
the  water  levels  about  the 
two  arms. 

Arrange  the  siphon  with 
a  small  difference  in  wa- 
ter level  as  shown  in  (1) 
Fig.  46  and  allow  the  wa- 
ter to  run  for  15  seconds ; 
then  arrange  it  with  a 
greater  difference  as  in 
(2)  Fig.  46  and  again  al- 
low the  water  to  run  for 
15  seconds. 


Does  more  water  flow  in 
(2)    than    in    (1),   that    is, 
is  the  velocity  greater  the 
greater    the    difference    in    a  Slphon' 
water  level? 


Fig.  46. — Velocity    of    Water    in 


OTHER  SIPHONS 

EXPERIMENT  No.  14 

To  make  and  operate  a  double  siphon  and  a  three  legged  siphon. 

Start  a  double  siphon,  (1)  Fig.  47.  Raise  the  tumblers  one  at  a 
time,  then  two  at  a  time. 

Does  the  water  always  flow  from  the  upper  tumbler  or  tumblers 
to  the  lower  and  does  it  always  stop  flowing  when  the  water  levels 
are  the  same? 

Start  a  three  legged  siphon,  (2)  Fig.  47  and  repeat  the  above  experi- 
ments. Are  the  results  the  same? 


Fig.   47. — Double   Siphon   and 
Three  legged    Siphon. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      29 


HOW  TO  START  A  SMALL  SIPHON 

EXPERIMENT  No.  15 

To  illustrate  two  ways  of  starting  a  small  siphon. 


Fig.  48.— Starting    a 
Small   Fountain. 


You  have  been  starting  your  small  siphon 
by  sucking  air  out  of  the  long  arm.  You 
can  also  start  it  as  shown  in  (1)  Fig.  48. 
Fill  the  siphon  with  water  to  force  the  air 
out,  close  the  ends  with  your  fingers,  in- 
vert the  siphon,  and  when  the  upper  end 
is  under  water  in  the  upper  tumbler  remove 
both  fingers,  (2)  Fig.  48. 

Glass  siphons  used  to  siphon  acid  have 
a  starting  tube  on  the  outside  arm,  (3) 
Fig.  48. 


Illustrate  the  use  of  this 
by  siphoning  water  out  of  a 
bottle  with  the  siphon  shown 
in  (4)  Fig.  48.  Place  the  up- 
per end  in  the  water,  close 
the  lower  end,  suck  out  a 
little  air,  and  open  the  lower 
end. 

Practice  until  you  can  start 
the  siphon  without  getting 
water  (representing  the  acid) 
on  your  fingers  or  lips. 


TO  UPS 


30      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


AN  ENCLOSED  FOUNTAIN 

EXPERIMENT  No.  16 

To  make  and  operate  an  enclosed  fountain. 


Arrange  the  apparatus  as  shown 
in  (1)  Fig.  49;  this  is  really  a 
siphon  with  a  bottle  at  the  top. 
Start  with  2  inches  of  water  in 
the  bottle,  insert  the  stopper  with 
tubes,  invert  the  whole  apparatus, 


Fig.  49. — An   Enclosed    Fountain. 

and  put  the  short  arm  in  the  tank 
filled  with  water. 

Does  the  water  run  and  is  there 
a  fountain  in  the  bottle? 

Arrange  the  apparatus  as  in  (2) 
Fig.  49,  lift  the  tank  until  there 
is  about  2  inches  of  water  in  the 
bottle,  then  arrange  as  shown. 

Is  there  a  fountain  in  the  bottle? 
Repeat  both  of  these  experiments 
but  use  instead  of  the  bottle,  a 
wide  glass  tube  closed  at  the  top 
with  a  solid  rubber  stopper,  (1) 
Fig.  50. 

Make  two  fountains  as  shown 
in  (2)  Fig.  50,  one  enclosed  and 
one  in  the  open. 


Fig.  50 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      31 


ATMOSPHERIC  PRESSURE 

You  have  made  a  number  of  experiments  with  siphons  and  you  have 
learned  how  they  act  under  different  circumstances;  you  will  now  make 
some  experiments  which  will  help  you  to  understand  "why"  they  act 
as  they  do. 

Water  moves  through  a  siphon  because  it  is  forced  to  do  so  by 
atmospheric  pressure.  You  will  first  make  a  number  of  experiments 
to  show  that  the  atmosphere  exerts  pressure  and  then  you  will  show 
how  and  why  this  atmospheric  pressure  forces  water  through  a  siphon. 


Fig.  51.— Weighing  Air. 


AIR  HAS  WEIGHT 

If  you  were  asked  the  question  "How 
much  does  air  weigh?",  you  would  prob- 
ably answer  off  hand,  "Air  has  no  weight 
at  all."  Air,  however,  has  considerable 
weight  and  it  would  take  a  very  strong 
man  indeed  to  carry  a  weight  equal  to 
that  of  the  air  in  a  house  of  medium  size. 

You  cannot  weigh  air  with  the  apparatus 
you  have  at  hand  but  this  is  how  it  is 
done.  The  apparatus  used  is  illustrated 

in  part  in  Fig.  51.  The  air  is  pumped  out  Courtesy" of  the^MacMilianCo. 
of  the  flask,  by  means  of  an  air  pump  (not  shown).  The  flask  is  then 
balanced  exactly  on  the  fine  scales  and  air  is  admitted  to  the  flask 
again.  It  is  found  that  the  flask  weighs  more  when  it  is  filled  with 
air  than  when  it  is  empty,  and  this  proves  that  air  has  weight. 

A  cubic  foot  of  air,  at  the  surface  of  the  earth  and  at  ordinary 
temperatures  is  found  in  this  way  to  weigh  about  1^4  oz.  This  is 
not  a  great  weight,  but  when  you  come  to  calculate  the  weight  of  air 
in  a  house  of  medium  size  you  find  that  it  amounts  to  a  very  great 
deal,  for  example,  make  the  following  calculation: 

A  house  with  a  flat  roof  is  40  feet  long,  by  30  feet  wide, 
by  24  feet  high;  find  the  weight  of  air  in  it,  neglecting  the 
space  occupied  by  partitions,  furniture,  etc. 


32      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


The  house  contains  40  x  30  x  24  —  28,800  cubic  feet  of  air,  and  since 
each  cubic  foot  of  air  weighs  1J4  ozs. — 

the  house  contains  28,800  x  1%  =  36,000  oz.  of  air,  and  since  there 
are  16  ozs.  in  1  lb. — 

36000 

the  house  contains   — — —  =  2250  Ibs.  of  air. 

16 

The  house  contains  2250  Ibs.  of  air  or  over  a  ton  of  air  (1  ton  = 
2000tbs).  This  is  a  very  astonishing  fact,  especially  to  those  of  us 
who  have  never  thought  of  air  as  having  any  weight  at  all. 


AIR  EXERTS  PRESSURE 

You  have  learned  from  your  lessons  in  Physical  Geography  at  school 
that  we  live  at  the  bottom  of  an  ocean  of  air  —  the  atmosphere  —  which 
is  many  miles  deep;  and  when  you  remember  that  a  cubic  foot  of 
air  weighs  1^4  °zs-  you  are  in  a  position  to  see  that  the  atmosphere 
must  exert  great  pressure  on  everything  at  the  earth's  surface. 

It  has  been  found  by  repeated  experiments  that  the  atmosphere 
exerts  a  pressure  of  14.7  Ibs.  (nearly  15  Ibs.)  on  each  square  inch  of 
everything  at  the  earth's  surface.  This  means,  for  example,  that  on 
every  square  inch  of  our  bodies  the  atmosphere  exerts  a  pressure  of 
14.7  Ibs.  We  might  think  that  this  would  crush  our  bodies,  until  we 
remember  that  everything  inside  our  bodies  exerts  the  same  pressure 
outward,  our  blood,  the  air  in  our  lungs,  etc. 

A  pressure  of  14.7  Ibs  per  square  inch  is  equal  to  the  pressure  at 
a  depth  of  34  feet  under  water,  that  is,  if  the  air  could  be  removed 
from  the  earth  and  be  replaced  by  water,  it  would  require  a  depth  of 
34  feet  of  water  all  over  the  earth  to  produce  a  pressure  equal  to  that 
produced  by  the  atmosphere,  namely,  14.7  Ibs.  per  square  inch. 

You  will  now  make  experiments  to  show  that  the  atmosphere  exerts 
pressure 

EXPERIMENT  No.  17 

To  show  that  the  atmosphere  exerts  pressure. 

Make  a  U  tube,  Fig.  52,  run  water  through  the  tube  until  all  the 
air  bubbles  are  gone,  then  empty  out  part  of  the  water  until  the  U 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      33 


is  a  little  more  than  half  full.    The  water  in  the  two  arms  is  then  at 
the  same  level. 


Now  apply  your  lips  to  the  coupling  on  one  arm, 
suck  out  the  air,  and  close  the  clip.  Do  you  observe 
that,  when  you  suck  out  the  air,  the  water  in  the 
open  arm  descends  while  that  in  the  other  arm 
rises? 

The  explanation  is  as  follows.  Everything  on 
the  earth  is  at  the  bottom  of  an  ocean  of  air  many 
miles  deep,  and  since  this  air  has  weight  it  exerts 
pressure  on  everything  on  the  earth.  Now  when 
both  arms  of  the  U  tube  are  open,  the  water  level 
is  the  same  in  both  and  the  pressure  of  the  air  on 
the  water  surface  in  each  is  the  same,  namely,  the 
pressure  of  the  atmosphere.  When  you  remove  the 
air  from  the  closed  side,  however,  you  remove  the 
pressure  of  the  atmosphere  from  this  side  and  the 
pressure  of  the  atmosphere  in  the  open  side  forces 
the  water  down  on  the  open  side  and  up  the  closed 
side.  This  experiment  shows  you  that  the  atmos- 
phere exerts  pressure. 

Repeat  and  make  experiments   of  your  own.        t 


Pressure. 


EXPERIMENT  No.  18 

To  show  that  the  atmosphere  will  support  a  column  of  water. 

Arrange  the  apparatus  as  in  (1)  Fig.  53,  fill  the  tube  with  water, 
close  one  end  with  a  clip  and  hold  both  ends  in  the  position  illustrated. 
Does  the  water  remain  in  the  tube?  It  remains  because  the  pressure 
of  the  atmosphere  downward  on  the  water  in  the  open  tube  supports 
the  column  of  water  in  the  long  tube. 

Turn  the  open  end  sidewise  and  then  downward.    Does   the  water 
remain  in  the  tube?     It  remains  because  the  atmosphere  exerts   pres- 
sure sidewise  and  upward  and  supports   the  water. 
A  — 3 


34      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


ATM. 


ATM 


t 

ATM. 

1  2  3 

Fig.  53.— Showing  That  the  Atmosphere   Will   Support   Water. 

Arrange  the  apparatus  as  shown  in  (2)  Fig.  53.  Place  the  lower  end 
of  the  tube  in  a  tumbler  of  water,  stand  on  a  chair,  and  suck  the  air 
out  of  the  tube,  then  close  the  upper  end. 

Does  the  water  remain?  It  remains  because  the  pressure  of  the 
atmosphere  downward  on  the  water  in  the  tumbler  supports  the  water 
in  the  tube. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      35 


Lift  the  tube  out  of  the  tumbler,  (3)  Fig.  53,  and  the  water  will 
remain  in  the  tube  because  it  is  supported  by  the  upward  pressure  of 
the  atmosphere.  This  is  possible  only  with  very  narrow  tubes.  The 
tube  you  have  used  in  these  experiments  is  about  6  feet  long  and 
you  have  shown  that  the  atmosphere  will  support  a  column  of  water 
6  feet  high.  If  you  had  a  tube  of  sufficient  length  you  could  show  that 
the  atmosphere  will  support  a  column  of  water  34  feet  high*  but  no  more. 


To  Air 
Pump  pr  Lipa 


Air 


To  Lipo 


To  Air 
Pump  or 


*i 

I 


1  3 

Fig.  54.— Proving  That  it  is  the  Atmosphere  Which  Lifts  the  Water. 


36       HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


EXPERIMENT    No.   19 

To  prove  that  it  is  the  pressure  of  the  atmosphere  which  lifts  the 
water. 

Make  a  U  tube  (1)  Fig.  54,  with  four  tubes  on  one  side  and  two  on 
the  other,  fill  it  half  full  of  water  so  that  the  two  tubes  on  the  short  side 
are  quite  full,  then  close  the  top  of  this  side  with  a  coupling  and  clip. 
Now  suck  the  air  out  of  the  long  side.  Do  you  observe  that  the  water 
does  not  move? 

It  does  not  move  because  although  you  have  decreased  the  air 
pressure  in  the  long  side,  the  atmosphere  cannot  get  at  the  water  in 
the  short  side  to  force  it  down. 

Open  the  top   and  repeat  the  experiment.    Does   the  water  move? 

To  show  this  in  another  way.    Fill  a  bottle  (2)  with  water,  place  a 

glass  tube  in  it  and  suck  the  air  out  of  the  tube.    You  observe  that  when 

you  remove  the  air  pressure  from  the  water  in  the  tube,  the  atmospheric 

pressure  on  the  water  in  the  bottle  forces  the  water  up  into  your  mouth. 

Now  fill  the  bottle  quite  full  to  exclude  the  air,  and  close  it  with  a 
one  hole  rubber  stopper  which  has  one  glass  tube  stuck  in  the  under 
side  and  another  in  the  upper  side,  (3).  Suck  the  air  out  of  the  upper 
tube.  Do  you  find  that  the  water  does  not  rise? 

It  does  not  rise  because  although  you  have  decreased  the  air  pres- 
sure in  the  upper  tube,  the  atmosphere  cannot  get  at  the  water  in  the 
bottle  to  force  it  into  your  mouth. 

You  have  proved  here  that  it  is  the  pressure  of  the  atmosphere 
which  lifts  the  water. 


EXPERIMENT  No.  20 

To  show  in  other  ways  that  the  atmosphere  exerts  pressure  down- 
ward and  upward. 

Fill  the  bottle  with  water,  close  the  top  with  the  hand,  invert  the  bottle 
in  a  pail  of  water,  and  remove  the  hand  under  water,  (1)  Fig.  55. 

The   downward   pressure    of   the   atmosphere   on    the  water   surface 
in  the  pail  supports  the  water  in  the  bottle. 

Repeat  with  the  tumbler  and  tube  as  shown  in   (2)  and  (3). 

Fill   the  bottle  with  water,   cover  with   a   piece   of  paper,  hold  the 
paper  on  with  the  hand,  invert  the  bottle  and  remove  the  hand,  (4). 

The  paper   is   held   on  by  the  upward  pressure  of  the  atmosphere. 

Repeat  this  experiment  with  a  tumbler  and  tube,  (5)  and  (6). 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING       37 


n 

ATM.  Arr-i. 

4  5 

Fig.  55. — Showing  That  the  Atmosphere  Exerts  Pressure  Downward  and  Upward. 

EXPERIMENT  No.  21 

To  illustrate  two  simple  uses  of  atmospheric  pressure. 

DRINKING  SODA  WATER 

When  you  drink  soda  water  through  a  straw  or  glass  tube,  (1)  Fig.  56, 
you  simply  produce  a  vacuum  in  your  mouth  and  it  is  the  atmosphere 
which  forces  the  soda  water  into  your  mouth. 

Illustrate  this  with  the  apparatus,  (2)  Fig.  56  in  which  the  bottle  repre- 
sents your  mouth.  Suck  air  out  of  the  bottle,  close  clip  1,  and  open 
clip  2. 

Does  the  atmosphere  force  water  into  the  bottle?     It  forces  soda 
water  into  your  mouth  in  the  same  way. 


38      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


POULTRY  DRINKING  FOUNTAINS 

Tb  Air         ** fcv  Fil1    a     tumbler    witn    water,    place     two 

Pllttlp  Or  Lip5  /5&      pieces  of  lead  pencil  across  the  top,  cover 
*     .a/      with    a    saucer,    and    invert    tumbler    and 
saucer,  (1)  Fig.  57. 
Repeat  with  the  glass  bottle,  (2). 
Does    the   water   run    out   only   until   the 
edge  of  the  tumbler  or  bottle  is  covered? 

Atm-         «  ToLii 


Attn. 


hiTnT 


To  imitate  the  poultry 
drinking  the  water,  suck 
water  out  of  the  saucer 
by  means  of  a  glass  tube 
until  the  water  is  below 
the  edge  of  the  tumbler. 


Does  air  enter  and  water  run  out  only  until  the 
edge   is   again   covered? 
The   atmosphere   supports   the  water. 
Note:     The    atmosphere   could   support   the   water 
in  a  fountain  34  feet  high  but  no  higher. 
Fig.  56.— Drinking  Soda  Water. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      39 


Fig.  57.— Poultry  Fountain. 
THE  SIPHON  (Continued) 

THE  "WHY"  OF  THE  SIPHON 


The  reason  "why"  water  flows 
through  a  siphon  is  as  follows : 
Suppose,  for  example,  you  have  a 
siphon,  Fig.  58,  closed  at  the  top 
with  a  clip.  The  atmospheric  pres- 
sure on  the  water  in  the  right  hand 
tumbler  supports  only  1  foot  of 
water,  while  in  the  left  hand  tumbler 
it  supports  two  feet  of  water. 

Now  the  atmospheric  pressure  on 
each  is  equal  to  the  pressure  of  a 
column  of  water  34  feet  high,  there- 
fore at  the  top  of  the  siphon  the 
pressure : 
at  the  right  of  the  clip  is 

34—1=  33  feet  of  water; 
at  the  left  of  the  clip  is 

34  —  2  =  32  feet  of  water. 

The  pressure  at  the  right  is  greater 
than  that  at  the  left  and  if  the  clip 
is  opened  the  water  flows  from  right 
to  left,  that  is,  from  the  upper  tumb- 
ler to  the  lower  tumbler. 

This  is  the  "why"  of  the  siphon. 


Fig.  58. — Showing  Why  the  Atmos- 
phere Drives  Water  Through  a  Siphon 


40      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


PUMPS 

EXPERIMENT  No.  22 

To  illustrate  the  action  of  a  syringe. 

The  simplest  kind  of  pump  is  the  syringe,  (A)  Fig.  59.  When  you 
lift  the  plunger,  there  is  a  vacant  space  or  partial  vacuum  left  below 
the  plunger  and  the  atmospheric  pressure  on  the  water  in  the  tumbler 
lifts  water  into  the  syringe. 


Courtesy    of 
The  MacMillan  Co. 


Illustrate  this  by 
means  of  the  syringe, 
fB)  Fig.  59.  Soap  the 
plunger  to  make  it 
slippery,  fill  the  syr- 
inge, lift  the  nozzle  end 
and  squirt  the  water 
.out,  (C)  Fig.  59, 


Fig.   59.—  The  Syringe 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      41 

WATER  GUN  SHOOTING 
GAME  No.  6 

The  syringe  makes  a  fine  water  gun.    Use  it  as  follows : 

(1)  Put  up  a  bent  piece  of  cardboard  as  a  target  and  try  to  hit  it  from 
various  distances,  (A)  Fig.  60. 

(2)  See  who  can  send  the  stream  to  the  greatest  height. 

(3)  See  who  can  send  the  stream  to  the  greatest  distance. 


Fig.  60  A.— Water  Gun  Shooting  and  Big  Gun  Battle. 

BIG  GUN  BATTLE 
GAME  No.  7 

Each  player  here  puts  up  the  same  number  of  lead  or  paper  soldiers 
and  at  a  given  signal  each  starts  to  knock  down  the  enemy  soldiers 
with  his  water  gun  which  here  represents  a  large  caliber  gun  firing 
shells,  (B),  Fig.  60. 

The  winner  is  the  one  who  first  knocks  down  all  the  enemy  soldiers. 


.Fig.   60  B. — Water  Gun  Shooting  and  Big   Gun   Battle, 


42      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


MACHINE  GUN  BATTLE 

GAME  No.  8 

Each  player  is  behind  a  barricade  which  represents  a  trench  (A), 
Fig.  61  and  is  armed  with  a  syringe  which  here  represents  a  machine 
gun.  The  rules  about  wounded  and  killed  are  the  same  as  in  Game 
No.  2.  The  winning  side  is  the  one  which  first  kills  all  the  enemy. 


Fig.  61  A.— Machine  Gun  Battle. 


THE  DIABLO  WHISTLE 

GAME  No.  9 

The  apparatus,  Fig.  61  B  makes  a  most 
uncanny  whistle  when  you  blow  into  it  as 
illustrated  and  move  the  plunger  up  and 
down. 

The  game  is :  (1)  to  make  the  most 
diabolical  sound  you  can ;  (2)  to  play  the 
eight  notes  of  an  octave  as  well  as  you 
can;  (3)  to  play  a  tune  if  you  can. 


Fig.  61  B.— The    Diablo    Whistle. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      43 


THE  LIFT  PUMP 

Common  pumps  are  of  two  kinds :  lift  pumps, 
Figs.  62,  63,  which  lift  water  only  to  the  spout;  and 
force  pumps,  Fig.  65,  which  force  the  water  to  any 
height  above  the  spout.  Both  types  of  pumps  have 
two  valves  which  open  upward. 

The  Lift  Pump,  Fig.  62,  has  one  valve  S  at  the 
bottom  of  the  barrel  C  and  another  V  in  the 
plunger  P.  The  atmospheric  pressure  lifts  water 
from  the  well  into  the  pump  through  the  suction 
pipe  T. 

The  way  the  lift  pump  lifts  water  is  illustrated 
in  drawings  1  to  6,  Fig.  63. 


Fig.  62.— A  Lift  Pump. 

Courtesy  of 
The  MacMillan  Co. 


(3) 


(4)  (5> 


(6) 


Fig.  63.  —  Showing  How  a  Pump  Raises  Water. 
Courtesy  of  The  MacMillan  Co. 


Before  the  pump  is  started  the  condition  is  that  shown  in  (1)  :  both 
valves  are  closed  and  the  water  level  in  the  suction  pipe  is  the  same 
as  that  in  the  well. 

When  the  plunger  is  raised  as  in  (2),  the  air  in  the  barrel  beneath 
the  plunger  is  given  more  room,  it  expands  and  its  pressure  on  the  valve 
S  is  decreased;  the  air  in  the  suction  pipe  then  lifts  the  valve  S  and  part 


44      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

of  it  expands  into  the  barrel;  this  decreases  the  air  pressure  on  the 
water  in  the  suction  pipe,  and  the  atmospheric  pressure  on  the  water 
in  the  well  forces  some  water  into  the  suction  pipe. 

When  the  plunger  is  shoved  down  as  in  (3),  valve  S  closes  and  the 
air  in  the  barrel  is  forced  up  through  the  plunger  valve  V. 

When  the  plunger  is  raised  again  as  in  (4),  the  operations  explained 
in  (2)  take  place  again,  and  the  atmospheric  pressure  on  the  water  in 
the  well  forces  more  water  into  the  suction  pipe  and  also  into  the  barrel. 

When  the  plunger  is  shoved  down  again  as  in  (5),  valve  S  closes 
again  and  all  the  air  in  the  barrel,  with  part  of  the  water,  is  forced  up 
through  the  plunger  valve  V. 

When  the  plunger  is  raised  again  as  in  (6),  the  water  above  the 
plunger  is  lifted  to  the  spout  and  the  atmospheric  pressure  on  the 
water  in  the  well  forces  more  water  into  the  suction  pipe  and  barrel. 

After  this  (5)  and  (6)  are  repeated  as  long  as  the  plunger  is  operated. 

EXPERIMENT  No.  23 

To  make  and  operate  a  Lift  Pump. 
Arrange  the  apparatus  as  shown  in  (1)  Fig.  64. 
Soap    the    plunger,    place    the    lower    end    of    the 
narrow  tube  in  a  glass  of  water,  and  move  the 
plunger  up   and   down   slowly. 

Do  you  find  that :  on  the  up  stroke  of  the 
plunger,  water  moves  up  through  the  narrow 
tube  and  lower  valve  into  the  pump  barrel;  and 
on  the  down  stroke,  the  water  remains  at  the 
same  height  because  the  lower  valve  closes,  but 
as  the  plunger  moves  down,  the  air  and  water 
pass  through  the  plunger  valve?  Do  you  no- 
tice that  on  the  succeeding  up  strokes,  water 
rises  and  flows  over  the  top,  and  on  succeeding 
down  strokes  it  moves  through  the  plunger 
valve? 

1  2 

Fig.  64. — The  Lift   Pump. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING       45 


Attach  three  or  four  narrow  tubes  below  the  pump  barrel  to  make 
the  suction  pipe  longer,  (2)  Fig.  64,  and  repeat  the  experiment. 

Attach  all  the  narrow  tubes  and  the  rubber  tube  to  the  pump  barrel 
and  repeat  the  experiment. 

Do  you  find  that  the  atmospheric  pressure  on  the  water  in  the 
tumbler  lifts  the  water  into  the  pump  barrel  when  you  move  the 
plunger  up? 

The  pressure  of  the  atmosphere  is  equal  to  the  pressure  of  a  column 
of  water  34  feet  high  and  no  more,  therefore,  a  pump  must  be  placed 
at  a  less  height  than  34  feet  above  the  water  it  is  pumping  and  in 
practice  the  height  is  usually  25  feet  or  less. 


THE  FORCE  PUMP 


The  force  pump,  Fig.  65,  has  a  valve  A 
at  the  bottom  of  the  barrel,  but  the  plun- 
ger V  is  solid,  the  discharge  pipe  leaves 
the  barrel  below  the  plunger,  and  the 
second  valve  B  is  below  an  air  chamber 
at  one  side;  also  the  top  of  the  barrel  is 
closed  by  an  inverted  U  shaped  leather 
ring  which  surrounds  the  plunger  and 
prevents  the  water  from  escaping. 

It  pumps  water  in  exactly  the  same 
way  as  does  the  lift  pump. 

The  ball  valves  shown  here  have  the 
advantage  that  they  wear  evenly  because 
they  turn  continuously.  Both  lift  pumps 
and  force  pumps  can  have  either  ball 
valves  or  common  flap  valves. 

The  air  chamber  protects  the  force 
pump  from  excessive  strain  because  the 
air  compresses  under  excessive  pressure; 
it  also  tends  to  keep  a  steady  stream  in 
the  discharge  pipe  because  the  compres- 
sed air  continues  to  force  the  water  out 
of  the  air  chamber  while  the  plunger  is 
making  the  up  stroke. 


Fig.  65.— Force  Pump  with  Solid 
Plunger   and    Ball   Valves. 
Courtesy  of  the  MacMillan  Co. 


46      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.   66. — The  Force  Pump. 

EXPERIMENT  No.  24 

To  make  and  operate  a  Force  Pump. 

Arrange  the  apparatus  as  shown  in  (1),  Fig.  66.  Soap  the  plunger, 
place  the  suction  pipe  in  a  tumbler  of  water,  pour  a  little  water  above 
the  plunger  to  make  sure  it  is  air  tight;  and  move  the  plunger  up  and 
down. 

Do  you  observe  that  on  the  up  stroke  water  enters  the  barrel  through 
the  valve,  and  that  on  the  down  stroke  it  is  forced  into  the  side  tube 
through  its  valve?  If  the  valves  are  not  quite  air  tight  pour  water  into 
both  tubes  to  cover  them. 

Make  an  air  chamber  in  the  side  tube  by  inserting  a  short  narrow 
glass  tube  below  the  upper  stopper,  (2),  Fig.  66. 

Operate  the  force  pump. 

Do  you  observe  that  the  air  is  slightly  compressed  in  this  chamber, 
on  the  down  stroke  of  the  plunger,  and  that  this  compressed  air  keeps 
the  water  flowing  for  a  short  time  after  the  stroke  is  finished. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      47 


Repeat  the  experiment  using  short  quick  strokes  of  the  plunger. 

Do  you  find  that  you  can  keep  a  fairly  steady  stream  issuing  from 
the  nozzle? 

Water  can  be  forced  to  any  height  in  the  discharge  pipe  of  a  force 
pump  but  the  suction  lift  should  not  be  more  than  about  25  feet,  that 
is  the  pump  plunger  must  be  within  25  feet  vertically  of  the  water  it  is 
pumping.  fi 


EXPERIMENT    NO    25 

To  show  how  water  is  pumped  into  an 
elevated  tank. 

A  lift  pump  can  be  used  to  pump  water 
into  an  elevated  tank  only  if  the  top  of  the 
tank  is  not  over  25  feet  (34  feet  theoreti- 
cally) above  the  water  in  the  well.  If  the 
tank  is  higher  than  this,  a  force  pump  must 
be  used. 

Illustrate  this  use  of  a  force  pump  by 
means  of  the  apparatus  shown  in  Fig.  67. 
Pump  water  into  the  tank  and  then  draw 
off  some  through  the  faucet  below.  This 
equipment  represents  a  complete  water 
supply  system. 

FORCE  PUMP  CONTEST 

GAME  No.  10 

The  game  here  is  to  see  who  can  force 
the  water  to  the  greatest  height  and  to  the 
greatest  distance.  Tie  the  stoppers  in  with 
cord  and  stretched  rubber  bands.  Use  the 
apparatus  shown  in  (2)  Fig.  66. 


Fig.  67. — Pump   Water  into   an 
Elevated  Tank  with  a  Force  Pump. 


48      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


HYDRAULIC  APPLIANCES 


The  hydraulic  press 
(A),  hydraulic  elevator 
(B).  and  hydraulic  lift 
lock  (C),  Fig.  68,  are 
each  operated  by  means 
of  pressure  exerted  on 
water,  and  in  order  to 
understand  them  you 
will  first  illustrate  Pas- 
cal's law  which  tells  how 
pressure  is  transmitted 
by  water. 


Fig.  68. — Hydraulic  Press,  Elevator  and  Lift  Lock. 

A— Courtesy  Ginn  &  Co.  B— Courtesy  of  The  MacMillan  Co. 

C—From  "Ontario  High  School  Physics"  by  Permission  of  the  Publishers 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      49 
PASCAL'S  LAW 


Fig.   69. — Illustrating  Pascal's  Law. 

Pascal's  Law  is:  Pressure  exerted  on  a  liquid  is  transmitted  equally 
and  undiminished  in  all  directions. 

This  law  is  usually  illustrated  by  means  of  the  apparatus  shown  in 
(1)  Fig.  69.  It  is  a  syringe  with  a  glass  bulb  which  has  five  nozzles  of  the 
same  size  and  in  the  same  plane.  When  the  syringe,  filled  with  water, 
is  held  with  the  nozzles  horizontal  and  the  plunger  is  forced  in,  the 
streams  which  issue  from  the  nozzles  are  of  exactly  the  same  length. 
This  shows  that  pressure  exerted  on  water  is  transmitted  equally  in  all 
directions.  This  is  very  surprising  because  since  the  plunger  exerts 
the  pressure  in  the  direction  of  the  front  stream  we  might  expect  this 
stream  to  be  the  longest:  we  find,  however,  that  they  all  have  the 
same  length. 

EXPERIMENT  No.  26 

To  show  that  pressure  on  water  is  transmitted  equally  in  all  directions. 
Use  the  apparatus   (2)  Fig.  69.    Fill  the  tube  with  water,  insert  fhe 
plunger,  hold  the  nozzles  horizontal,  and  force  the  plunger  in_steadily, 
Are  the  streams  of  equal  length? 
A  — 4 


50      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


200 


100  Ibs 

uuufimj 

71 

6. 

.  '^t/t&ff's 

l»q.  in. 

____--^-__  —  —  :3- 

-—  —  —  __—  _=  — 

Repeat  with  the  apparatus  (3)  Fig.  69. 

With  (2)  Fig.  69  you  show  that  the  pressure  is  transmitted  equally 
forward  and  sidewise,  and  with  (3)  Fig.  69,  that  it  is  transmitted  equally 
in  both  sidewise  directions. 

This  experiment  shows  that  water  transmits  pressure  equally  in  all 
directions.  The  experiments  described  below  show  that  it  transmits  it 
equally  and  undiminislied  in  all  directions. 

The  two  cylinders  and  connect- 
ing pipe,  Fig.  70,  are  filled  with 
water  and  each  cylinder  is  fitted »«  in. 
with  a  water  tight  piston ;  the  area 
of  cross  section  of  the  small  piston 
is  1  sq.  in.  and  of  the  large  piston, 
100  sq.  in.  If  now  a  pressure  of 
1  Ib  is  exerted  on  the  small  piston,.  Fig>  70_A  Pregaure  0£  One  Pound 

it     is     found    that    this    pressure     is     on   a    Small    Piston    Exerts   a    Lift   of   One 

Hundred  Pounds   on  a   Large  Piston. 
Courtesy  of  The  MacMillan  Co. 

transmitted  equally  and  undiminished  by  the 
water,  and  that  therefore,  the  upward  pressure 
on  the  large  piston  is  1  ft),  on  each  sq.  in.  or  the 
total  pressure  upward  is  100  ft>s.  That  is,  1  Ib. 
on  the  small  piston  supports  100  Ibs.  on  the  large 
piston. 

This  is  very  surprising  and  it  looks  as  if  we 
were  getting  something  for  nothing.  This  is  not 
so,  however,  because  if  the  small  piston  is  moved 
down  1  inch,  the  large  piston  moves  up  only  1/100 
of  an  inch.  That  is,  "what  is  gained  in  iorce  is 
lost  in  distance  moved." 

The  hydrostatic  bellows,  Fig.  71,  is  an  appar- 
atus of  this  kind  and  it  illustrates  Pascal's  law 
beautifully.  It  consists  of  two  disks  of  wood 
connected  by  a  water-proof  canvas  cylinder  to 
make  a  collapsible  drum.  A  small  pipe  passes 

Fige  71. The  Hydrostatic   tnrougn  the  lower  disk  and  opens  into  the  drum. 

Bellows.  The  Smalt  Amount  If  now  the  drum  is  filled  with  water  and  a  man 
of  Water,  AB,  Supports  a  stands  on  the  upper  disk,  it  is  found  that  a  very 
Man's  Weight.  small  amount  of  water,  AB,  in  the  pipe  will  sup- 

his  weiht- 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      51 

This  is  very  striking  and  it  is  explained  as  above.  If,  for  example, 
the  area  of  the  pipe  is  1  sq.  in.  and  that  of  the  disk  is  500  sq.  in.  then 
1  ft),  of  water  in  AB  will  support  a  weight  of  500  Ibs.  on  the  disk. 
Similarly  y2  lb.  of  water  in  AB  will  support  J^  x  500  =  250  Ibs.  on 
the  disk,  or  J4  Ibs.  of  water  in  AB  will  support  %  x  500  =  125  Ibs.  on 
the  disk,  and  so  on. 


EXPERIMENT  No.  27 

To  make  and  operate  a  hydrostatic  bellows. 

Arrange  the  apparatus  as  shown  in  Fig.  72.  Place  the  book  on  the 
empty  observation  balloon,  and  fill  the  balloon  with  water  until  it  is 
about  half  full.  Do  you  observe  that  a  very  little  water  in  the  tube 
supports  the  weight  of  one  end  of  the  book. 

Place  an  empty  tumbler  on  the  book 
and  fill  it  with  water.  Do  you  find  that 
a  small  extra  amount  of  water  in  the 
tube  supports  the  glass  of  water? 

Remove  the  tumbler  and  press  down 
on  the  book  with  your  hand.  Do  you 
find  that  to  lift  water  in  the  tube  you 
must  exert  a  force  much  greater  than 
the  weight  of  this  water. 

These  experiments  are  certainly  very 
striking  and  they  illustrate  Pascal's  law 
as  follows :  The  weight  of  the  extra 
water  in  the  tube  exerts  pressure  down- 
ward on  an  area  equal  to  that  of  the 
inside  of  the  tube;  this  pressure  is  trans- 
mitted equally  and  undiminished  in  all 
directions  by  the  water,  and  is  exerted 
against  each  equal  area  of  the  inside 


Fig.  72.— Illustrating  the   Hydro- 
static  Bellows. 


of  the  balloon. 


52      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


THE  HYDRAULIC  PRESS 


The  hydraulic  press  is  an  application 
of  Pascal's  law  and  of  the  hydrostatic 
bellows.  It  is  used  where  great  pressure 
is  required,  for  example,  to  compress 
merchandise,  to  bend  ship  plates,  to  lift 
great  weights,  and  so  on. 

The  press  has  a  force  pump  with 
handle  P  which  operates  the  small  pis- 
ton A  in  the  small  cylinder  C  and  pumps 
water  from  the  reservoir  L  through  the 
valve  d,  through  the  connecting  pipe 
and  valve  v,  and  into  the  large  cylinder 


Fig.  73.— The   Hydraulic  Press. 
Courtesy  of  The  MacMillan  Co. 


so  on. 


D.    The  large  piston  B,  or  ram  as  it  is  called,  moves  up  and  down  in  D. 
Both  A  and  B  have  collars  which  prevent  the  escape  of  water. 

If  now  the  end  of  ram  B  has  an  area  100  times  as  great  as  the  end 
of  A,  then  each  1  Ib.  exerted  on  A  exerts  a  lift  of  100  Ibs.  on  B,  and 

EXPERIMENT  No.  28 
To  make  and  operate  a  hydraulic  press. 
Arrange  the  apparatus  as  shown  in  Fig.  74,  where 
the  tin  can  in  the  tank  represents  the  ram  and  where 
the  balloon  represents  the  collar  of  the  ram.    Soap 
the  plunger  to  make  it  slippery. 

Open  lower  clip,  raise  the  plunger,  close  lower  clip, 
open  side  clip  and  lower  the  plunger.  Repeat  until 
the  balloon  is  partly  filled  with  water. 

Now  fill  the  tin  can  with  water  and  repeat  the 
operations  above. 

Do  you  find  that  a  small  force  on  the  plunger  will 
lift  the  relatively  large  weight  of  the  tin  can  full  of 
water? 

You  have  shown  here  that  on  the  hydraulic  press 
a  small  force  moving  the  small  piston  a  long  dis- 
tance lifts  a  great  weight  on  the  large  piston  a 
small  distance. 


Fig.  74. — Illustrating 
the  Working  of  a 
Hydraulic  Press. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING   53 


THE  HYDRAULIC  ELEVATOR 

The  simplest  form  of  hydraulic  elevator  is  illustrated 
in  Fig.  75.  The  passenger  cage  A  is  securely  fastened  to 
the  top  of  a  long  ram  P  which  moves  up  and  down  1*1  a 
deep  cylinder  C.  The  elevator  is  raised  by  the  city  water 
pressure  or,  if  this  pressure  is  not  sufficient,  by  the  pres- 
sure of  water  pumped  into  a  tank  on  the  roof  of  the 
building.  The  water  enters  through  the  pipe  m  and 
through  the  three-way  valve  if,  and  it  leaves  through  the 
three-way  valve  and  the  lower  pipe. 

The  weight  of  the  cage  and  ram  is  partly  counter- 
balanced by  the  weight  shown.  When  water  is  admit- 
ted to  the  cylinder,  it  exerts  pressure  upward  on  the 
bottom  of  the  ram  and  raises  the  ram  and  cage;  when 
the  discharge  pipe  of  the  cylinder  is  opened,  the  cage 
and  ram  descend  by  their  own  weight  and  drive  the 
water  out  of  the  cylinder. 


The    operation    of    the    three-way 
valve  is  illustrated  in  Fig.  76.    The 
lever  handle  is  weighted  at  the  end 
and  is  operated  by  the  cord  t,  t,  c,  c, 
which     passes     through     the     cage. 
When   the   operator   pulls    the   cord 
up  the  valve  takes  the  upper  posi- 
tion,    water     is     admitted     to     the 
cylinder,  and  the  ram  and  cage  are  dragg  ge 
raised.       When    the    operator   pulls 
the  cord  down,  the  valve  takes  the   "Millikan&  Gale's 
Fig.  76.—  The  Three-  lower    position    and    connects    the         First  Course 
way  Valve.  cylinder    with    the    discharge    pipe; 

From  the  cage  and  ram  then  descend  by 

"Millikan&  Gale's    their  own  weight  and   in   doing  so 
First  Course  ,  f 

in  Physics."         force    water    from    the    cylinder    to 

By  Permission  of       th      sewer 
Ginn  &  Co.,  Pub.      Ine   sewer, 


—The  Hy- 


° 


in  Physics.' 
By  Permission  of 
Ginn  &  Co.,  Pub. 


54      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


When  speed  is  desired,  for  example  in  carrying 
passengers,  the  elevator  is  arranged  as  shown  in 
Fig.  77.  The  plunger  or  ram  P  moves  in  a  cylin- 
der C.  Both  ram  and  cylinder  carry  a  number 
of  large  separate  pulleys,  side  by  side,  around 
which  a  steel  cable  is  passed  a  number  of  times 
and  then  attached  to  the  counterpoise  weight  D. 

If,  for  example,  the  steel  cable 
makes  10  loops  around  the  pulleys 
there  are  20  strands  between  the 
two  sets  of  pulleys.  If  then  the 
ram  moves  1  foot  each  strand  is 
lengthened  1  foot  and  the  counter- 
poise is  pulled  down  20  feet.  Since 
the  cable  attached  to  the  passen- 
ger cage  passes  around  the  pulley 
of  the  counterpoise  as  shown,  each 
foot  the  counterpoise  descends 
raises  the  cage  2  feet.  Thus  if  the 
ram  moves  1  foot,  the  counter- 
poise moves  20  feet  and  the  cage, 
40  feet.  This  gives  the  passenger 
cage  a  speed  forty  times  that  of 
the  ram. 


Fig.  77.— A  Rapid  Hydraulic 
Elevator  for  Passengers. 
From  "Millikan   &   Gale's 
First  Course  in  Physics." 

By  permission  of 
Ginn   6-  Co.,  Publishers 


The  Tarn  is  moved  by  water  from  the  city 
mains  which  is  controlled  by  a  three-way  valve 
as  described  above. 


Fig.  78.— Illustrating 
the  Working  of  a  Hy- 
draulic Elevator. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      55 


EXPERIMENT  No.  29 

To  make  and  operate  a  hydraulic  elevator. 

Arrange  the  apparatus  as  shown  in  Fig.  78.  Soap  the  plunger  well 
to  make  it  slippery. 

Open  side  clip.    Is  the  cage  raised?     Close  side  clip.    Does  it  stop? 

Open  lower  clip  and  press  down  gently  on  the  cage.  Does  it  descend? 
Close  lower  clip.  Does  it  stop? 

Now  open  and  close  side  clip  to  raise  the  cage  a  short  distance  at  a 
time.  Do  you  find  that  you  control  the  elevator  perfectly  as  it  rises? 

Now  open  and  close  lower  clip  while  you  force  the  cage  down  a  short 
distance  at  a  time.  Do  you  find  that  you  can  control  the  elevator 
perfectly  as  it  descends  and  that  you  cannot  move  it  down  when  the 
clip  is  closed? 

You  have  shown  here  how  the  ram  and  cage  of  an  elevator  are 
raised  by  water  pressure  and  how  they  descend  by  their  own  weight. 
You  have  shown  also  that  you  can  stop  them  anywhere,  while  rising  or 
descending,  by  closing  the  proper  valve. 

HYDRAULIC  LIFT  LOCKS 
CANAL  LOCKS 


Fig.  79.— A  Single  Lock. 
Courtesy  of  "The  Scientific  American' 


56      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

An  ordinary  canal  lock,  Fig.  79,  is  used  to  raise  or  lower  steamers 
a  few  feet  to  enable  them  to  pass  up  or  down  stream,  around  a  rapid, 
dam  or  waterfall.  It  is  simply  a  short  canal  with  a  pair  of  gates  at 
each  end. 

If  the  steamer  is  going  up  stream,  it  sails  through  the  lower  gates 
of  the  lock;  the  lower  gates  are  closed  behind  it;  water  is  admitted  to 
the  lock  until  its  level  is  equal  to  that  of  the  water  above  the  lock;  the 
upper  gates  are  then  opened,  and  the  steamer  sails  out  of  the  lock 
at  the  upper  level.  If  the  steamer  is  going  down  stream  the  reverse 
operation  takes  place. 

If  the  difference  in  level  is  considerable  but  over  some  distance,  a 
number  of  these  locks  are  used,  for  example,  if  the  difference  in  level 
were  80  feet  in  a  distance  of  two  miles,  there  might  be,  in  the  two  miles, 
4  locks  with  a  difference  of  level  of  20  feet  each  or  8  locks  with  a  differ- 
ence of  10  feet  each,  and  so  on. 

When  the  difference  in  level  is  great  in  a  short  distance,  however, 
a  lift  lock  must  be  used. 

LIFT  LOCKS 

Lift  locks  are  so  called  because  the  whole  lock,  with  the  water  in 
it  and  the  ship,  is  lifted  vertically  from  the  low  level  to  the  high,  or 
is  lowered  vertically  from  the  high  level  to  the  low.  They  are  always 
in  pairs  and  the  weight  of  one  balances  the  weight  of  the  other. 

The  lift  lock  shown  in  Fig.  80,  is  one  that  it  is  proposed  to  build 
on  a  canal  between  Lake  Erie  and  Lake  Ontario.  It  will  take  ships 
650  feet  long  and  of  30  foot  draft,  and  will  lift  or  lower  them  through  a 
vertical  height  of  208  feet.  The  inner  side  of  one  will  be  connected 
with  the  inner  side  of  the  other  by  56  steel  cables  which  pass  over  56 
sheaves  of  20  foot  diameter.  The  outer  side  of  each  will  be  connected 
with  large  concrete  counterweights  by  means  of  steel  cables  passing  over 
56  sheaves  on  each  side.  The  locks  will  be  raised  and  lowered  by  means 
of  electrical  power  applied  to  the  rims  of  each  sheave.  The  gates  at 
the  ends  of  each  lock  and  at  the  ends  of  the  upper  and  lower  canal  will 
be  opened  and  closed  by  being  moved  down  and  up  vertically.  The 
diagram  shows  how  the  locks  will  look  when  one  ship  is  being  raised 
and  another  lowered.  The  building  at  the  right  is  a  plant  in  which 
electrical  power  will  be  developed  from  the  excess  water  from  the  upper 
canal.  A  small  part  only  of  this  power  will  be  used  to  operate  the  locks. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      57 


Fie.  80.— A  Proposed  Lift- Lock.  Courtesy  of  "The  Scientific  American' 


58      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


HYDRAULIC  LIFT  LOCKS 

Hydraulic  lift  locks 
are  so  called  because 
they  are  operated  by 
means  of  water.  Each 
lock  is  a  large  steel 
tank  securely  attached 
to  the  top  of  a  very 
large  ram  which  moves 
up  and  down  in  a  deep 
cylinder.  The  two  cylin- 
ders are  connected  by 
a  pipe  through  which 
the  water  flows  from 
one  to  the  other,  the 
flow  being  controlled, 
or  stopped  entirely,  by 
means  of  a  valve. 


Fig.  81.— The    Hydraulic    Lift-Lock. 


ig.  81.— The    Hydraulic    Lift-Lock 

From   the   "Ontario   High  School 

Physics."     By   permission  of 

the  Pubishers. 

The  operation  of  the  locks  will  be  un- 
derstood from  Fig.  82.  If  the  steamer 
is  going  up  stream :  it  sails  into  the  lock 
B  which  is  down  and  the  lock  gate  is 
closed;  a  little  water  is  admitted  to  the 
lock  A  which  is  up,  to  make  it  weigh 
more  than  the  lower  lock  B  and  the 
steamer;  the  valve  R  is  opened;  the 
upper  lock  descends  and  its  ram  Pi 
forces  water  from  its  cylinder  into  that 
of  the  lower  lock;  the  pressure  of  this 

water  raises  the  ram  P2,  the  lower  lock 
Fte.  82.— Showing     How    Lift-Locks 
Operate.  and  the  steamer,  to  the  upper  level;  the 

From  the  "Ontario  High  School  Physics."  eates  are  opened;  and  the  steamer  sails 

By  Permission  of  the  Publishers 

out  at  the  upper  level. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      59 


If  the  steamer  is  going  down  stream;  it  sails  into  the  upper  lock 
and  the  gates  are  closed;  water  is  admitted  to  the  upper  lock  to  make 
it  weigh  more  than  the  lower  lock;  the  valve  R  is  opened;  water  is 
forced  from  the  cylinder  of  the  upper  lock  to  that  of  the  lower  as  the 
upper  lock  descends  and  the  lower  lock  rises;  the  gates  are  opened; 
and  the  steamer  sails  out  at  the  lower  level. 

Note.  You  might  think  that  the  presence  of  the  steamer  in  one  lock 
would  make  it  weigh  more  than  the  other  lock,  but  you  will  learn  in 
Experiment  36  that  a  ship  displaces  its  own  weight  of  water  and  that 
therefore  the  one  lock,  plus  water,  plus  steamer,  weighs  the  same  as 
the  other  lock  plus  water. 


EXPERIMENT  No.  30 

To  make  and  operate  a  hydraulic  lift  lock. 

Use  the  apparatus  shown  in  Fig.  83.  The  wide  tubes  and  plungers 
represent  the  cylinders  and  rams  of  a  real  lift  lock,  and  the  clip  repre- 
sents the  control  valve.  The  inverted  tumblers  represent  the  locks, 
they  should  of  course  be  right  side  up  but  you  have 
no  way  of  fastening  them. 

Place  a  button  or  pebble  on  the  lower  lock  to 
represent  a  ship,  open  the  clip  and  press  down  on 
the  upper  lock.  Is  the  ship  raised? 

Lower  a  steamer  in  the  same  way. 

Now  place  a  steamer  in  the  lower  lock  and  press 
down  on  the  upper  lock  while  you  open  and  close 
the  clip  from  time  to  time.  Do  you  find  that  the 
plungers  stop  as  soon  as  you  close  the  clip? 

This  shows  how  the  rams  of  a  real  lift  lock  can 
be  stopped  anywhere  by  closing  the  valve  R,  Fig.  82. 
Water  is  incompressible,  as  you  know  from  Exper- 
iment, No.  7,  and  when  valve  R  is  closed  the  rams 
cannot  move  because  the  water  in  the  cylinders 
cannot  be  compressed  and  cannot  move. 

Repeat  this  but  close  the  clip  only  partly. 

Do  you  find  that  the  plungers  can  move  slowly       Fig.  83.— Hlustrat- 
and  that  you  can  regulate  the  speed  by  opening    gf 
the   clip  more   or   less?  Lock. 


60      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

This  shows  how  the  rams  in  a  real  lift  lock  can  be  allowed  to  move 
rapidly  or  slowly  by  opening  the  valve  R  more  or  less 

In  this  experiment  you  have  illustrated  the  working  of  a  hydraulic 
lift  lock:  you  have  shown  that  the  downward  movement  of  one  ram 
drives  water  into  the  second  cylinder  and  that  the  pressure  of  this  water 
raises  the  ram  in  the  second  cylinder;  you  have  shown  also  that  the  rams 
can  be  stopped  anywhere  by  closing  the  valve  R  or  that  they  can  be 
made  to  move  very  slowly  by  closing  the  valve  partly. 


THE  PRESSURE  EXERTED  BY  WATER 


Fig.  84.— The  Height  of  the  Stream  is  Independent  of  the  Size  or  Shape  of  the 
Tank  and  Pipe. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      61 

A  very  astonishing  fact  is  illustrated  in  Fig.  84,  namely  that  the 
pressure  at  the  nozzles  is  the  same  no  matter  what  size  and  shape  the 
tank  may  be  and  no  matter  what  size  and  shape  the  pipe  may  be, 
provided  the  water  level  in  the  tank  is  at  the  same  distance  above 
the  nozzle  in  all  cases.  You  will  now  prove  this. 

EXPERIMENT  No.  31 

To  show  that  the  pressure  at  a  nozzle  is  independent  of  the  size 
and  shape  of  the  tank  and  pipe. 


Fig.  85. — Showing  That  the  Pressure  at  a  Nozzle  is  Independent  of  the  Size  or 
Shape  of  the  Tank  or  Pipe. 

Make  the  experiments  illustrated  in  Fig.  85  one  after  the  other  using 
the  same  nozzle  in  all.  Are  the  streams  of  the  same  height  in  all  cases 
if  the  water  level  in  the  tank  is  at  the  same  distance  above  the  nozzle? 


62      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


You  have  shown  here  that  the  pressure  exerted  by  water  is  inde- 
pendent of  the  volume  of  the  water  but  that  it  depends  upon  the  height 
of  the  water  above  the  nozzle.  This  is  known  as  the  Hydrostatic 
Paradox  which  you  will  now  illustrate. 


THE  HYDROSTATIC  PARADOX 

The  Hydrostatic  Paradox  is  stated  as  follows  :  The  pressure  exerted 
by  a  liquid  on  any  base  is  independent  of  the  volume  of  the  liquid,  but 
depends  only  on  the  area  of  the  base,  the  depth  of  the  liquid,  and  the 
density  of  the  liquid. 

Note.  The  density  of  a  liquid  is  its  weight  per  cubic  foot,  or  per 
cubic  inch,  or  per  cubic  centimeter. 

The  hydrostatic  paradox  is  illustra- 
ted by  means  of  the  apparatus  shown 
in  Fig.  86.  The  three  tops  are  of  diff- 
erent sizes  and  shapes,  but  they  fit  a 
common  base.  The  bottom  of  this 
base  is  covered  by  a  sheet  of  rubber 
or  by  a  sheet  of  corrugated  metal. 
The  base  sinks  as  the  pressure  in- 
creases and  moves  the  pointer,  which 
indicates  the  pressure. 

If  the  tops  are  screwed  to  the  base, 
one  after  the  other,  and  then  filled 
with  water  to  the  same  height,  the 

Fig.  86.— Illustrating  the  Hydrostatic   pointer  indicates  the  same  pressure  in 
Paradox.  _ii  ,.„--- 

Courtesy  of  The   MacMillan  Co.         a11  cases- 

The  volume  of  water  in  the  tops  is  different  in  each  case,  but  the 
pressure  is  the  same  in  all.  This  shows  that  the  pressure  exerted  by 
a  liquid  is  independent  of  the  volume  of  the  liquid,  provided  the  area  of 
the  base,  the  depth  and  the  density  of  the  liquid  are  the  same  in  all  cases. 

Another  form  of  this  apparatus  is  shown  in  Fig.  87;  the  three  tops 
fit  the  same  base,  but  the  bottom  is  a  brass  plate  AB  which  is  held  on 
by  a  cord  attached  to  one  arm  of  a  balance  (not  shown).  The  plate  AB 
falls  in  each  case  when  the  water  reaches  the  same  height. 

The  hydrostatic  paradox  is  also  illustrated  in  4;  the  three  tubes  are 
of  very  different  volumes  but  the  water  stands  at  the  same  height  in  all. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      63 


Fig.  87. — A  Second  Method  of  Illustrating  the  Hydrostatic  Paradox 
Courtesy  of  The  MacMillan   Co. 

These  experiments  show  that  the  pressure  a  liquid  exerts  on  a  given 
base  is  independent  of  the  volume  of  the  liquid,  provided  the  area  of 
the  base,  depth  of  the  liquid,  and  density  of  the  liquid  are  constant. 


EXPERIMENT  No.  32 

To   illustrate   the   hydrostatic  paradox. 


B  C 

Fig.  82,— Illustrating   the    Hydrostatic    Paradox. 


64      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

Make  the  experiments  A,  B  and  C,  Fig.  88,  one  after  the  other.  Is 
the  water  in  the  small  tube  always  at  the  same  height  as  that  in  the 
funnel  or  large  tube? 

Arrange  the  apparatus  as  in  D,  Fig.  88.  Is  the  water  at  the  same 
level  in  all  cases? 

The  funnel  and  wide  tube,  each  contain  more  water  than  the  small 
tube;  nevertheless,  the  downward  pressure  of  the  water  in  each  is  bal- 
anced by  the  downward  pressure  of  the  water  in  the  small  tube. 

You  have  shown  here  that  the  pressure  exerted  by  a  liquid  is  inde- 
pendent of  the  volume  of  the  liquid,  that  is,  you  have  illustrated  the 
hydrostatic  paradox. 

EXPLANATION  OF  THE  HYDROSTATIC  PARADOX 

The  hydrostatic  paradox  seems  impossible,  and  that  is  why  it  is 
called  a  paradox.  It  would  seem  to  be  self  evident  that  the  greater 
the  volume  of  water  above  a  base,  the  greater  would  be  the  pressure; 


ijB 


Fig.  89. — Explanation  of  the  Hydrostatic  Paradox. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      65 

and  the  less  the  volume,  the  less  the  pressure.  You  have  shown  above, 
however,  that  the  pressure  on  a  given  base  is  independent  of  the  volume 
of  water  and  that  it  depends  only  on  the  depth. 

The  paradox  is  explained  as  follows  : 

In  1,  Fig.  89,  the  base  AB  is  subject  to  the  pressure  of  the  water  in 
the  cylinder  above  it,  and  in  this  case,  the  pressure  is  equal  to  the 
weight  of  the  water. 

In  2,  Fig.  89,  the  same  base  AB  has  a  much  larger  volume  of  water 
above  it  but  the  pressure  is  the  same  as  in  1.  You  will  understand 
why,  if  you  consider  the  water  outside  the  dotted  lines.  This  water 
exerts  a  force  perpendicular  to  the  sides  of  the  cone,  and  another  force 
horizontally  against  the  water  between  the  dotted  lines,  see  the  arrows. 
Neither  of  these  forces  has  any  effect  downward  on  the  base  and  there- 
fore the  base  is  subject  only  to  the  weight  of  the  water  between  the 
dotted  lines.  This  weight  is  the  same  as  in  1  and  therefore  the  pressure 
on  AB  is  the  same  as  in  1. 

In  3,  Fig.  89,  the  base  AB  has  a  much  smaller  volume  above  it  than 
in  either  1  or  2,  but  still  the  pressure  is  the  same  as  in  1  and  2.  You 
will  understand  why  from  your  knowledge  of  Pascal's  law.  The  water 
above  AB  is  exerting  pressure  downward,  and  according  to  Pascal's 
law  this  pressure  is  transmitted  equally  and  undiminished  in  all  di- 
rections. The  pressure  per  square  inch  downward  on  the  whole  of  AB, 
therefore,  is  equal  to  what  it  would  be  if  the  whole  space  between  the 
outer  dotted  lines  were  filled  with  water.  This  pressure  is  equal  to  that 
in  (1)  and  this  is  why  the  pressure  in  (3)  is  equal  to  that  in  (1). 

HOW  TO  CALCULATE  THE  PRESSURE 
EXERTED  BY  WATER 

The  density  (weight)  of  fresh  water  is  62l/2  Ibs.  per  cubic  foot  and 
if  in  (1)  Fig.  89,  the  base  AB  is  1  square  foot  and  the  height  of  the 
water  is  10  feet,  there  are  10  cubic  feet  of  water  in  the  tank  and  the 
total  pressure  on  the  bottom  is  10  x  62.5  =  625  Ibs. 

Since  the  pressure  exerted  by  water  is  independent  of  the  volume  of 
the  water  and  depends  only  on  the  area  of  the  base,  the  height,  and  the 
density  of  the  water,  the  pressure  on  AB  in  (2)  and  (3)  is  625  Ibs.,  the 
same  as  in  (1). 

The  rule  for  calculating  the  pressure  in  any  case  is :  Pressure  on 
any  base  =  area  of  base  in  square  feet  x  height  of  water  in  feet  x 
density  of  water  (weight  of  1  cubic  foot)  or,  Pressure  =  area  x  height 
x  density. 

A  — 5 


66      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


In  the  example  given : 

Pressure  =  1  x  10  x  62.5  =  625  Ibs.  per  square  foot. 

To  find  the  pressure  per  square  inch,  first  find  the  pressure  per  square 
foot  and  then  divide  the  result  by  144,  the  number  of  square  inches  in 
1  square  foot.  For  example,  the  pressure  on  1  square  inch  of  AB  in 
any  of  the  tanks  illustrated  is  625  -r-  144  =  4.34  Ibs. 

PRESSURE  UNDER  WATER 
THE  DEPTH  BOMB  —  TORPEDO  —  SUBMARINE 


THE  DEPTH  BOMB 


90.— The  Depth  Bomb. 


Courtesy  of  "The  Scientific  American" 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      67 

The  depth  bomb  is  used  by  submarine  chasers  to  destroy  submarines. 
It  is  a  steel  cylinder  filled  with  high  explosives  and  equipped  with  a 
trigger  which  sets  off  the  explosive  at  any  desired  depth  under  water. 

The  trigger  is  released  by  means  of  a  small  plunger  which  is  exposed 
to  the  pressure  of  the  sea  water  on  the  outside  and  is  supported  by  a 
spring  on  the  inside.  The  pressure  of  the  water  increases  as  the  bomb 
sinks  and  forces  the  plunger  in  farther  against  the  spring,  but  the 
spring  can  be  so  adjusted  that  at  any  desired  depth  the  plunger  releases 
the  trigger  and  the  bomb  explodes. 

When  the  chaser  sights  a  submarine  it  steams  for  it  and  if  it  is 
still  above  water,  attacks  it  with  guns;  but  if  it  has  submerged,  the 
chaser  steams  in  circles  around  the  spot  where  it  disappeared  and  drops 
or  fires  bombs  adjusted  to  explode  at  different  depths. 

THE  TORPEDO 


WADHCAD 


U001A  CQ*T*Ql* 


Fig.  91. — The  Principle  Parts  of  the  Torpedo. 

Reproduced  by  Permission  from  the  "Boy's  Book  of  Submarines"  by  Frederick  Collins. 
Copyright  by  Frederick  A.  Stokes  Co. 


The  torpedo  is  a  cigar  shaped  tube 
loaded  in  the  head  with  high  explo- 
sives which  are  set  off  by  a  contact 
pin.  It  is  driven  by  means  of  a  com- 
pressed air  motor  and  is  steered  by 
horizontal  and  vertical  rudders. 

We  are  interested  in  the  horizontal 
rudder  particularly  at  this  point.  It 
steers  the  torpedo  to  a  depth  of  20 
feet  under  water  and  keeps  it  at 
this  depth.  It  does  this  by  means 
of  the  pressure  of  the  sea  water.  The 
horizontal  rudder  is  controlled  by  a 
piston,  Fig.  92,  which  is  exposed  to 
the  pressure  of  the  sea  water  on  the 


Mt/Z*  *>tSt<S*t  Of  iQFftt 


Fig.  92.— The  Torpedo  is  Kept  at  a 
Depth  of  20  feet  by  Water  Pressure. 
Reproduced  by  Permission  from  the 
"Boy's  Book    of   Submarines." 

by  Frederick   Collins. 
Copyright  by  Frederick  A.  Stokes  Co. 


68      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


outside  and  is  supported  by  a  spring  on  the  inside.  This  piston  and 
its  spring  are  so  adjusted  that  at  20  feet  under  water  the  rudder  is 
exactly  horizontal,  but  at  a  greater  or  less  depth  the  rudder  is  so  turned 
as  to  bring  the  torpedo  back  to  a  depth  of  20  feet. 


THE  SUBMARINE 


Fig.  93. — The  Submarine. 

Reproduced  by  Permission  from  the  "Boy's  Book  of  Submarines"  by  Frederick  Collins. 
Copyright  by  Frederick  A.  Stokes  Co. 

The  submarine  must  be  able  to  stand  enormous  pressures  when  under 
water  and  for  this  reason  it  is  made  in  the  shape  of  a  cylinder  with 
pointed  ends,  because  this  curved  shape  enables  it  to  stand  greater 
pressure  than  it  could  if  its  sides  were  flat;  also  it  is  made  of  steel 
because  this  is  the  strongest  material  available. 

You  cannot  experiment  with  the  depth  bomb,  torpedo,  and  submarine, 
of  course,  but  you  can  make  experiments  to  illustrate  the  water  pressure 
under  which  they  operate.  You  can  show  that  the  pressure  under  water 
increases  with  the  depth,  that  it  is  equal  in  all  directions  at  any  depth, 
etc.,  and  this  you  will  now  do. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      69 


EXPERIMENT  No.  33 

To  show  that  the  pressure  under 
water  increases  with  the  depth  and 
that  it  is  equal  in  all  directions  at 
any  given  depth. 

This  is  usually  shown  by  means 
of  the  apparatus  A,  Fig.  94.  The 
U  shaped  bend  of  the  three  tubes 
contain  mercury  to  the  same  depth. 
Both  ends  of  the  tubes  are  open. 
The  short  ends  point  upward,  side- 
wise  and  downward  respectively. 
When  the  short  ends  of  these  tubes 
are  lowered  in  water,  the  mercury 
shows  that  the  pressure  increases 

is 


A — Courtesy   of 

The  MacMillan   Co. 

B  and  C—Frotn    the 

"Ontario    High   School 

Physics."    By    permission  with     the     depth,     and     that     it 
of  the   Publishers 

equal  in  all  directions  at  any  given 


depth. 


1  2 

Fig.  95. — The  Pressure  is  Equal  in  All  Directions  at  any  Given  Depth. 


70      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

This  fact  is  illustrated  in  another  way  by  means  of  the  apparatus, 
B  and  C,  Fig.  94.  A  thistle  tube  covered  by  a  sheet  of  rubber  is  placed 
under  water  and  the  water  in  the  U  tube  indicates  a  greater  pressure  the 
greater  the  depth.  If  the  thistle  tube  is  turned  in  all  directions  at  any 
given  depth,  the  water  in  the  U  tube  shows  that  the  pressure  is  equal 
in  all  directions  at  this  depth. 

Illustrate  these  facts  by  means  of  the  apparatus,  Fig.  95. 

Shove  the  funnel  straight  down  (1).  Does  the  pressure  increase  with 
the  depth? 

Turn  the  funnel  sidewise  (2)  and  upward  at  any  depth.  Is  the 
pressure  equal  in  all  directions  at  any  given  depth? 


EXPERIMENT  No.  34 

To  show  that  water  exerts  pressure  upward  on  any- 
thing under  its  surface  and  that  the  upward  pressure 
is  equal  to  the  downward  pressure  at  any  given  depth. 

This  is  usually  shown  with  the  apparatus  Fig.  96.  If 
a  glass  lamp  chimney  A,  is  fitted  with  a  thin  ground 
glass  bottom  O  which  is  held  over  one  end  by  a  thread 
C,  while  this  end  is  placed  in  water,  it  is  found  that 


Fig.  96.— The  Up- 
ward Pressure  at  any 
Point  Under  Water  is 
Equal  to  the  Down- 
ward Pressure  at  this 
Point. 

Courtesy  of 
The  MacMillan  Co. 


the  bottom  remains  on  when 
the  thread  is  released.  This 
shows  that  water  exerts  pres- 
sure upward  on  anything  un- 
der its  surface. 

If  now  water  is  poured  in- 
to the  chimney,   the  bottom 


Fig.  97.— Showing  That 
the  Pressure  Upward  and 
Downward  are  Equal  at 
any  Depth. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      71 

remains  on  until  the  level  inside  the  chimney  is  the  same  as  the  level 
outside  and  this  is  true  at  any  depth.  This  shows  that  the  pressure 
upward  at  any  depth  under  water  is  equal  to  the  pressure  downward 
of  the  column  of  water  inside  the  chimney.  In  other  words,  it  shows 
that  the  pressure  upward  at  any  depth  under  water  is  equal  to  the 
pressure  downward  at  this  depth. 

Illustrate  this  with  the  apparatus  (1)  Fig.  97.  Put  the  stoppered  end 
in  water.  Is  a  fountain  produced  and  does  the  flow  stop  when  the 
level  inside  is  equal  to  that  outside  the  tube? 

Use  the  apparatus  (2)  Fig.  97,  hold  the  rubber  sheet  on  until  it  is 
under  water.  Does  it  remain? 

Pour  water  into  the  tube.  Does  the  sheet  fall  off  when  the  level 
inside  is  equal  to  that  outside? 

You  have  shown  here  that  water  exerts  pressure  upward  against 
anything  under  its  surface  and  that  the  upward  pressure  is  equal  to 
the  downward  pressure  at  any  given  depth. 

HOW  TO  CALCULATE  THE  PRESSURE  ON  DEPTH  BOMB, 
TORPEDO  AND  SUBMARINE 

Sea  water  is  heavier  than  fresh  water;  it  weighs  64  Ibs.  per  cubic 
foot  while  fresh  water  weighs  only  62l/2  Ibs.  per  cubic  foot. 

DEPTH  BOMB 

A  depth  bomb  is  set  to  explode  at  a  depth  of  250  feet.  If  sea  water 
weighs  64  Ibs  per  cubic  foot,  what  is  the  pressure  per  sq.  in.  against  the 
plunger  at  this  depth? 

Note:  Calculate  the  pressure  per  square  foot  and  divide  this  by 
144,  the  number  of  square  inches  in  one  square  foot. 

Pressure  =  Area  X  depth  X  densi'tv- 
144 

_,  1  x  250  x  64 

Pressure  = rrr =  111.1  lb.  per  sq.  in. 

TORPEDO 

A  torpedo  is  set  to  travel  at  a  depth  of  15  feet  under  water.  What 
is  the  pressure  per  sq.  in.  on  the  steering  plunger  at  this  depth? 

T,  Area  x  depth  x  density. 

Pressure  =- ^n * 

144 

1  x  15  x  64 
Pressure  = rrr =  6.6  Ibs.  per  sq.  in. 

SUBMARINE 

What  is  the  pressure  per  square  foot  on  the  outside  of  a  submarine 
at  an  average  depth  of  150  feet  in  water? 
Pressure  =  Area  x  depth  x  density. 
Pressure  —  1  x  150  x  64  =  9600  Ibs.  per  sa.  ft. 


72      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


BUOYANCY 

WHY  DOES  A  STEEL  SHIP  FLOAT? 


Fig.  98.— Why  Does  This  Steel  Ship  Float? 
Courtesy  of  "The  Scientific  American" 

Modern  ships  are  made  of  steel,  example,  the  superdreadnaught 
shown  in  Fig.  98,  and  although  steel  is  over  seven  times  as  heavy  as 
water,  bulk  for  bulk,  steel  ships  float.  Why  is  this? 

You  know  the  answer,  at  least  partly.  You  know  that  if  a  ship 
were  a  solid  lump  of  steel,  it  would  sink.  You  know  also  that  a  ship 
is  hollow,  except  for  its  equipment,  and  that  this  hollowness  in  some 
way  enables  it  to  float. 

The  true  reason  is  that  the  ship  as  a  whole  is  lighter  than  an  equal 
volume  of  water. 

You  will  show  in  the  following  experiments  that  water  exerts  a 
buoyant  force  on  anything  placed  in  it,  and  that  as  a  result:  things 
which  are  lighter  than  an  equal  volume  of  water  float  on  water;  while 
things  which  are  heavier  than  an  equal  volume  of  water  sink  but  are 
lighter  under  water  than  above  water. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      73 


Fig.  99. — Illustrating  the  Buoyant  Effect  of  Water. 

EXPERIMENT  No.  35 

To  illustrate  the  buoyant  effect  of  water. 

Find  about  your  home  an  empty  tin  can  with  a  tight  lid.  Submerge 
it  partly  as  in  (1)  and  release  it.  Does  it  shoot  upward?  This  buoyant 
effect  of  the  water  is  due  to  the  upward  pressure  of  the  water. 

Submerge  it  entirely  as  in  (2)  and  (3)  and  release  it.  Does  it  shoot 
upward?  This  buoyant  effect  shows  that  the  upward  pressure  of  the 
water  on  the  under  side  of  the  can  is  greater  than  its  downward  pressure 
on  the  top  side. 

Fill  the  can  with  water,  submerge  and  release  it.  Does  it  sink? 
Lift  the  full  can  under  water  and  out  of  water.  Is  it  much  lighter 
when  under  water?  It  is  lighter  because  the  water  buoys  up  part  of 
its  weight. 

THE  LAW  OF  ARCHIMEDES 

The  exact  law  which  applies  to  the  buoyancy  of  liquids  was  dis- 
covered by  a  Greek  philosopher  Archimedes  200  years  before  the  Christ- 
ian era  began.  It  is  called  the  law  of  Archimedes  and  it  is  as  follows  : 
the  buoyant  force  exerted  by  a  liquid  on  a  body  immersed  in  it,  is 
exactly  equal  to  the  weight  of  the  liquid  displaced  by  the  body. 

It  is  also  stated  more  concisely  as  follows :  a  body  when  placed 
in  a  liquid  appears  to  lose  weight  equal  to  the  weight  of  liquid  it 
displaces. 


74      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  100. — The  Cup  and  Cylinder.     One  Method  of  Illustrating  the  Law  of  Archimedes. 
Courtesy   of  The   MacMillan   Co. 


The  law  of  Archimedes  is  illustrated  by  means  of  the  apparatus 
shown  in  Fig.  100.  The  solid  cylinder  A  is  so  made  that  it  just  fits 
the  cup  B,  that  is,  the  cylinder  has  exactly  the  same  volume  as  the  cup. 

The  experiment  is  as  follows:  The  cylinder  A  is  attached  to  the 
bottom  of  the  cup  B  and  both  are  suspended  from  one  pan  of  a  balance. 
Weights  are  added  to  the  other  pan  until  the  cup  and  cylinder  are 
just  balanced. 

If  then,  a  vessel  of  liquid  is  raised  up  under  the  cylinder  A  until 
it  is  completely  submerged,  the  cup  and  cylinder  appear  to  lose  weight 
because  the  liquid  buoys  up  the  cylinder.  If  now  the  cup  B  is  filled 
with  the  liquid,  the  balance  is  exactly  restored. 

Now  the  weight  of  the  liquid  which  fills  the  cup  is  equal  to  that 
of  the  liquid  displaced  by  the  cylinder  and  therefore  this  experiment 
proves  the  law  of  Archimedes,  namely,  the  buoyant  force  exerted  by 
a  liquid  on  a  body  immersed  in  it  is  equal  to  the  weight  of  the  liquid 
displaced  by  the  body. 

The  law  of  Archimedes  is  also  illustrated  by  means  of  the  apparatus 
shown  in  Fig.  101  and  by  means  of  a  spring  balance,  not  shown. 

The  body  is  first  weighed  on  the  spring  balance  in  air,  then  in  the 
liquid,  and  the  apparant  loss  in  weight  in  the  liquid  is  determined. 

The  vessel  with  the  spout  is  then  filled  with  the  liquid  until  it  over- 
flows, the  body  is  placed  in  the  liquid,  and  the  liquid  displaced  is  weighed. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      75 


Fig.   101.— Another   Method   of   Illus- 
trating  the    Law   of   Archimedes. 
Courtesy  of  The  MacMillan  Co. 


The  apparent  loss  in  weight  of 
the  body  is  then  compared  with  the 
weight  of  liquid  displaced  by  the  body, 
and  it  is  found  that  in  every  case 
they  are  equal. 

You  will  now  make  experiments 
to  illustrate  the  law  of  Archimedes 
for  bodies  which  float  on  water  and 
for  bodies  which  sink  in  water,  also 
you  will  illustrate  some  of  the  appli- 
cations of  this  law. 


Fig.   102.   (1)— A  Ship  Unloaded. 


Fig.   102.   (2)— The  Same  Ship  When  Loaded. 


76      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


A  ship  is  a  floating  body  and  it  displaces  its  own  weight  of  water. 
If,  for  example,  a  ship  weighs  10,000  tons  it  displaces  10,000  tons  of  water. 
If  5000  tons  of  cargo  are  added  it  floats  deeper  in  the  water  and  displaces 
15,000  tons  of  water,  and  so  on. 

You  will  now  show  that  a  floating  body  displaces  its  own  weight  of 
water. 

EXPERIMENT  No.  36 

To  illustrate  the  law  of  Archimedes  for  bodies  which  float. 


Use  the  empty  glass 
bottle  as  the  floating 
body.  Close  the  lower 
hole  in  the  metal  tank 
with  a  No.  1  stopper,  put 
the  large  coupling  in  the 
upper  hole,  fill  the  tank 
with  water  until  water 
runs  out  through  the 
coupling  and  stops.  (l)Fig. 
103.  Now  place  the  bottle 
slowly  in  the  water  and 
catch  the  water  it  dis- 
places, (2)  Fig.  103. 


Fig.  103.— A  Floating 

Body  Displaces  Its  Own 

Weight   of   Water. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      77 


Now  make  a  spring  balance  with  a  bucket,  (3),  Fig.  103,  as  follows : 
Find  a  tin  can  around  your  home,  punch  two  nail  holes  near  the  top, 
and  attach  the  can  to  the  elastic  band  by  means  of  a  cord,  suspend 
the  band  from  a  nail  driven  in  a  piece  of  board. 

Now  put  the  bottle  in  the  can  and  mark  the  position  of  the  bottom 
of  the  elastic  band.  Then  take  the  bottle  out  and  pour  into  the  can 
the  water  displaced  by  the  bottle,  (4),  Fig.  103.  Do  you  find  that  the 
displaced  water  weighs  the  same  as  the  bottle,  that  is,  that  a  floating 
body  displaces  its  own  weight  of  water? 

You   have   here    illustrated 
the    law   of   Archimedes    for 


Fig.  104  - 1.— A  Body  Which 
Sinks  Loses  Weight  Equal 
to  the  Weight  of  Water  it 
Displaces. 

bottom  of  the  rubber 
band  again,  then  pour 
the  displaced  water  in- 
to the  can,  (4).  Does 
the  balance  descend  to 
the  mark  (2)  ?  That  is, 
is  the  buoyant  effect  on 
the  bottle  equal  to  the 
weight  of  the  water 
displaced  by  the  bottle? 


floating   bodies. 

EXPERIMENT  No.  37 

To  illustrate  the  law  of 
Archimedes  for  bodies  which 
sink  in  water. 

Use  the  bottle  filled  with 
water  to  represent  a  body 
which  sinks  in  water,  fill  the 
metal  tank,  Fig.  104,  with 
water  until  it  overflows 
through  the  coupling  and 
stops.  Place  the  bottle  in  the 
tank  slowly  and  catch  the 
water  it  displaces. 

Now  attach  the  full  bottle 
to  the  bottom  of  the  balance 
(2)  and  mark  the  position 
of  the  bottom  of  the  rubber 
band.  Submerge  the  bottle 
in  water  (3),  mark  the  posi- 
tion of  the 


78      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


You  have  here  illustrated  the  law  of  Archimedes   for  bodies  which 
sink  in  water. 


•l\  !)'•* 

I 


Fig.  104-3  Fig.  104-4 

A  Body  Which  Sinks  Loses  Weight  Equal  to  the  Weight  of  Water  It  Displaces. 


RAISING  SUNKEN  SHIPS 
EXPERIMENT  No.  38 

To  show  how  sunken  ships  are  raised  by  means  of  air. 

Sunken  ships  are  raised  by  compressed  air  as  illustrated  in  Figs.  105 
and  106.  Air  is  pumped  into  the  ship  until  the  ship  and  the  air  displace 
a  weight  of  water  slightly  more  than  the  weight  of  the  ship ;  the  buoyant 
force  of  the  water  then  lifts  the  ship  to  the  surface. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      79 


Fig.  105. — Pumping  Air  into  a  Sunken  Ship  to  Force  the  Water  Out. 


Illustrate  this  with  the  apparatus  shown  in  (1),  Fig.  107.  Fill  the 
bottle  with  water  to  represent  the  sunken  ship,  submerge  it  in  a  pail 
of  water,  and  blow  air  in  through  the  hose.  Does  the  ship  float  to  the 
surface? 

Sunken  ships  are  also  raised  by  means  of  large  steel  pontoons  filled 
with  air  as  shown  in  Fig.  108. 

Illustrate  this  as  shown  in  (2),  Fig.  107.  Use  the  bottle  as  the 
sunken  ship  and  two  empty  tin  cans  of  the  same  size  as  the  pontoons. 
Punch  nail  holes  in  the  opposite  sides  of  the  top  edge  of  each  tin 
can,  connect  them  as  shown,  force  air  into  them  a  little  at  a  time 
in  equal  amounts.  Is  the  ship  raised  nearly  to  the  surface? 


80      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  106. — Showing  How  the  Washingtonian  was  Raised  by  Compressed  Air. 
Courtesy  of  "The  Scientific  American" 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      81 


Fig.   107. — Showing  How  Ships  are  Raised  by  Compressed  Air. 


Fig.  108.— Showing  How  Ships  are  Raised  by  Means  of  Large  Steel  Pontoona 

Courtesy  of  "The  Scientific  American" 
A  — 6 


82      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Note:  The  ship  would  be  floated  into  shallow  sheltered  water  in 
this  way,  then  repaired  by  divers,  and  floated  by  compressed  air  as 
described ;  or  a  coffer  dam  would  be  built  around  it  and  the  water 
pumped  out;  then  the  repaired  ship  would  float  when  the  water  was 
admitted  to  the  dam. 


FLOATING  DRY  DOCKS 

The  floating  dry  dock,  Fig.  109,  is  a  huge  steel  or  concrete  trough 
shaped  structure  with  hollow  sides  and  with  large  tanks  along  the 
bottom.  It  is  open  at  both  ends  and  when  the  tanks  T.T.T.,  Fig.  110  are 
filled  with  water  it  sinks  to  the  water  line  L.L.  The  boat  then  sails 
into  the  dock  and  is  securely  braced,  the  water  is  pumped  out  of  the 
tanks  T.T.T.,  the  dock  rises  until  the  water  line  is  at  W.W,,  and  lifts 
the  ship  above  water. 

The  dry  dock  lifts  its  own  weight  and  the  weight  of  the  ship~be-; 
cause  it  displaces  a  weight  of  water  equal  to  the  combined  weights. 


Fig.  109. — Floating  Dry  Dock 
Courtesy  of  "The  Scientific  American" 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      83 


When  the  ship  has  been  repaired 
or  when  the  barnacles  have  been 
scraped  from  its  bottom  and  it  is 
ready  for  sea,  water  is  again  ad- 
mitted to  the  tanks,  the  dock  sinks 

to  the  water  line  LL,  and  the  ship 

., 
sails   out. 

Fig.  110.— Cross  Section  of  Floating  Dry        You   will    now   make    an    experi- 

Dock    and    Ship. 
Courtesy  of  The  MacMillan  Co.  ment   to   illustrate   the  working  of 

a  floating  dry  dock. 

EXPERIMENT  No.  39 

To  make  and  operate  a  floating  dry  dock. 


Use  a  flat  cake  pan  to  represent 
the  dry  dock,  and  the  bottle  to 
represent  the  ship. 

Float  the  dock  on  water  in  a 
sink  or  wash  basin  and  pour  water 
into  it  until  it  floats  with  the  top 
about  1  in.  above  water.  This  re- 
presents the  real  floating  dry  dock, 
with  its  tanks  full,  ready  to  receive 
the  ship. 

Float  the  bottle  on  the  water  in 
the  dock.  This  represents  the  ship, 
in  the  dock  and  ready  to  be  raised. 


Fig.  111. — Illustrating    the    Working   of   a 
Floating    Dry    Dock. 


Now  siphon  the  water  out  of  the  dry  dock  and  over  the  edge  of 
the  sink  or  wash  basin.  This  represents  the  water  being  pumped  out 
of  the  tanks  of  a  real  dry  dock.  Do  you  observe  that  both  the  dock 
and  the  ship  are  raised  as  the  water  is  siphoned  out?  This  shows 
how  the  dock  and  ship  are  raised  when  the  water  is  pumped  out  of  the 
tanks  of  a  real  dry  dock. 

Now  siphon  water  from  the  sink  into  the  floating  dry  dock.  Do 
you  observe  that  the  dock  and  the  ship  sink  as  water  enters  the  dock? 
This  represents  how  the  real  dock  sinks  when  water  is  admitted  again 
to  the  ballast  tanks. 


84      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

THE  GLASS  SUBMARINE 

EXPERIMENT  No.  40 

To  make  the  glass  submarine  submerge  and  rise  in  water. 


Fig.   112.— The  Glass   Submarine. 


You  will  observe  that  the  glass  submarine  (1),  Fig.  112,  is  hollow  and 
that  it  has  a  hole  at  the  stern. 

Place  it  in  a  tumbler  of  water.    Does  it  float? 

Place  it,  stern  down,  in  the  bottle  full  to  overflowing  with  water, 
close  the  bottle,  turn  it  on  its  side,  and  shove  the  stopper  in  hard. 
Does  the  submarine  submerge?  Withdraw  the  stopper  slightly.  Does 
the  submarine  rise  and  also  mpve  forward  suddenly? 

Repeat  this  with  the  bottle  between  your  eyes  and  a  light  and  observe 
the  air  in  the  submarine.  Is  the  air  compressed  when  you  shove  the 
stopper  in,  and  does  it  expand  when  you  withdraw  the  stopper? 

The  submarine  floats  in  the  tumbler  because  it  is  lighter  than  an 
equal  volume  of  water.  It  sinks  in  the  bottle  when  you  force  the 
stopper  in  because  sufficient  water  is  forced  in  to  make  it  heavier  than 
an  equal  volume  of  water.  It  rises  when  you  release  the  stopper  because 
the  air  expands  and  forces  sufficient  water  out  to  make  it  again  lighter 
than  its  own  volume  of  water. 

Water  is  nearly  incompressible  but  air  is  very  compressible  and 
when  you  shove  the  stopper  in  you  compress  the  air  but  not  the  water. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      85 


Find  a  larger  bottle  and 
repeat  these  experiments. 

The  submarine  moves  for- 
ward when  you  withdraw  the 
stopper  because  the  expand- 
ing air  shoots  a  stream  of 
water  to  the  rear  through 
the  stern  and  this  drives  the 
submarine  forward. 

Illustrate  this  with  the  ap- 
paratus Fig.  113.  Does  the 
stream  in  one  direction  un- 
der water  force  the  nozzle  in 
the  other  and  make  it  writhe 
like  a  snake? 


Fig.  113. — The  Water  Issuing  from  the  Nozzle 
in  One  Direction  Drives  the  Nozzle  in  the  Other 
Direction. 


RUNNING  WATER 
FRICTION 

As  soon  as  water  starts  to 
run  in  a  pipe  it  rubs  against  the 
inside  of  the  pipe  and  its  veloc- 
ity is  decreased.  This  rubbing 
is  called  friction  and  it  always 
decreases  the  flow  of  water. 

EXPERIMENT  No.  41 

To  illustrate  the  effect  of  fric- 
tion on  running  water. 

Use  the  appar- 
atus, (1),  Fig. 
114.  Raise  and 
lower  the  tank. 
Do  you  find  that 
the  stream  from 
the  nozzle  never 
reaches  the  level 
of  the  water  sur- 
face in  the  tank? 


1  2 

Fig.  114. — Friction    Decreases    the   Height   of   Streams. 


1 


86      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


It  does  not  do  so  because  the  friction  in  the  tubes 
and  nozzle  decrease  its  velocity. 

Use  the  apparatus  (2),  Fig.  114.  Is  the  lower  stream 
longer  than  the  upper,  but  do  you  find  that  it  does 
not  reach  as  high  as  the  upper  stream?  It  does  not, 
because  the  velocity  of  the  water  in  the  lower  tube  and 
nozzle  is  greater  and  therefore  the  friction  is  greater. 
Use  the  apparatus,  Fig.  115.  Allow  the  water  to  run  into 
the  tumbler  for  exactly  15  seconds  and  observe  the 
amount,  then  close  the  coupling  above  the  tee,  empty  the 
water  back  into  the  tank,  transfer  the  elbow  to  the  end 
coupling,  and  allow  the  water  to  run  into  the  tumbler  from 
the  end  for  exactly  15  seconds.  Is  the  flow  of  water  less 
from  the  end?  It  is  less  because  the  friction  in  the 
extra  pipes  decreases  its  velocity. 

It  is  a  matter  of  the  greatest  importance  that  friction 
be  taken  into  consideration  in  planning  the  piping  for 
any  system  of  water  supply  or  water  power.  The  facts 
regarding  it  may  be  stated  briefly  as  follows : 


Fig.  115. — Showing  That  Friction  Decreases  the  Velocity  of  Water  in  Pipes. 


The  friction  of  water  in  pipes : 

(1)  Is  greater  in  long  pipes  than  in  short  pipes  of  the  same  size. 

(2)  Is  greater  in  rough  pipes  than  in  smooth  pipes  of  the  same  size. 


(3) 

f4)     Is  greater  in  small  pipes  than  in  large  pipes  of  the  same  length. 


Is    greater  when    the   water    is    moving   rapidly    than   when   it    is 
moving  slowly  . 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      87 
NOZZLES 


Fig.   116. — Boy  Puts  More  Water  on  the  Road  in  a  Given  Time  Without  a   Nozzle 

Than  With  One. 

When  you  have  been  watering  the  road  or  garden  you  have  probably 
noticed  that  the  stream  is  longer  when  you  use  a  nozzle  than  when  you 
simply  let  the  water  flow  from  the  end  of  the  hose.  Have  you  noticed, 
however,  that  you  put  less  water  on  the  road  or  garden  in  a  given 
time  with  a  nozzle  than  without? 

EXPERIMENT  No.  42 

To   show  why  the   stream  is   longer  with  a  nozzle   than  without. 

Use  the  apparatus  (1),  Fig.  117.  Is  the  stream  short  and  is  the 
pressure  low?  Place  a  nozzle  in  the  coupling  (2),  Fig.  117.  Is  the  stream 
long  and  is  the  pressure  high? 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  117  -  1. — The  Pressure  is   Low  Behind  a  Large  Nozzle. 
Fig.  117  -  2. — The  Pressure  is  High  Behind  a  Small  Nozzle. 


You  have  shown  here  that  the  stream  from  a  nozzle  is  longer  than 
from  the  hose  because  the  pressure  behind  it  is  greater. 

The  pressure  at  any  point  in  a  pipe  carrying  running  water  is 
proportional  to :  first,  the  height  above  the  point  of  the  water  in  the 
tank;  and  second,  to  the  fraction  of  the  total  resistance  the  running 
water  encounters  beyond  the  point.  The  pressure  behind  the  nozzle 
in  (2)  is  great  because  the  resistance  the  water  encounters  in  the  nozzle 
is  great. 

EXPERIMENT  No.  43 

To  show  that  you  put  less  water  on  a  road  in  a  given  time  with  a 
nozzle  than  without. 

Use  the  apparatus,  Fig.  118,  allow  the  water  to  run  from  the  end 
of  the  hose  into  the  tumbler  for  exactly  15  seconds  and  observe  the 
amount,  then  insert  the  nozzle  and  repeat.  Is  the  flow  less  with  the 
nozzle  than  without? 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      89 


VELOCITY  OF  FLOW 

T" 


Fig.   118.— Less    Water 
Flows  in  the  Given  Time 
With  a  Nozzle  Than 
Without. 


'~The  Vdocity  of  Flow  is  Double  Wh«i  the  Head  is  Made  Four  Times 


90      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


You  might  think  that  the  velocity  of  water  from  a  nozzle  would  be 
doubled  when  you  double  the  height  of  the  water  in  the  tank  above 
the  nozzle.  You  will  show,  however,  that  you  must  make  the  height  four 
times  as  great  to  double  the  velocity. 

EXPERIMENT  No.  44 

To  show  that  the  velocity  of  water  is  doubled  when  the  head  is 
made  four  times  as  great. 

Use  the  apparatus,  Fig.  119.  Allow  the  water  to  flow  into  the  tumbler 
for  15  seconds  with  the  head  exactly  one  foot,  observe  the  amount  care- 
fully, then  repeat  with  the  head  exactly  four  feet.  Is  the  amount  doubled? 

The  head  is  the  vertical  distance  the  water  surface  in  the  tank  is 
above  the  nozzle  opening. 

The  velocity  of  water  in  a  pipe  varies  as  the  square  root  of  the  head. 
That  is,  if  you  start  with  a  head  of  1  foot,  and  increase  the  head  to  4 
feet  the  velocity  is  doubled,  V^  =  2;  if  you  increase  the  head  to  9  feet 
the  velocity  is  trebbled  -^9  =  3,  and  so  on. 


AIR  LOCK 


Fig.  120. — Showing   How   an   Air 
Lock  Occurs  in  a  Supply  Pipe. 


If  the  pipe  from  your  water  tank 
to  your  house  runs  up  and  down  hill, 
it  may  become  stopped  by  an  air 
lock  as  shown  in  Fig.  120.  In  (1)  the 
tank  is  empty  but  water  remains  in 
the  U  part  to  the  level  of  the  bath- 
room faucet;  above  this  is  air.  In  (2) 
the  tank  is  again  filled  and  the  bath- 
room faucet  is  open  but  the  water 
does  not  run.  It  does  not  because 
the  air  in  the  pipe  permits  the  IS 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      91 


Fig.   120. — Showing    How    an   Air 
Lock  Occurs  in  a  Supply  Pipe. 


Fig.    121.— Illustrating   an   Air-Lock 
in  Pipes 


foot  head  at  the  tank  to  be  balanced 
by  the  15  foot  head  below  the  bath- 
room faucet.  This  is  called  an  air- 
lock. 

The  air  lock  can  be  destroyed  by 
opening  any  faucet  near  the  bottom 
of  the  U  because  these  let  out  the 
water  and  then  the  air.  It  can  be 
destroyed  here  by  opening  the  base- 
ment faucet. 

EXPERIMENT  No.  45 

To  illustrate  an  air  lock. 

Use  the  apparatus,  Fig.  121.  In  (1) 
the  tank  is  empty  and  the  U  is  half 
full  of  water.  In  (2)  the  tank  is  filled 
but  the  water  does  not  run.  It  is 
air  locked  because  the  air  permits  the 
8  inch  head  in  the  U  to  balance  the 
8  inch  head  at  the  tank. 

Open  the  tee.  Is  the  air  let  out? 
Close  the  tee.  Does  the  water  flow, 
that  is,  is  the  air  lock  destroyed.? 


92      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


PNEUMATIC  ENGINEERING 

Pneumatic  engineering  is  the  engineering  which  deals  with 
air  and  other  gases.  You  have  already  used  two  pneumatic 
appliances  in  the  section  on  hydraulic  engineering,  namely,  the 
siphon  and  the  pump;  these  are  pneumatic  and  also  hydraulic 
appliances.  You  have  also  made  some  experiments  to  show 
that  the  atmosphere  exerts  pressure ;  you  will  begin  your  work 
in  pneumatic  engineering  by  making  further  experiments  along 
this  line. 


ATMOSPHERIC  PRESSURE 

EXPERIMENT  No.  46 

To  show  that  the  atmosphere  exerts  pressure. 

The  Magdeburg  hemispheres,  (1)  Fig.  122,  are  made  of  metal,  are 
hollow,  and  are  ground  smooth  around  the  edge  so  that  they  fit  to- 
gether air-tight.  When  the  air  is  pumped  out,  through  the  handle  on 
one  side,  they  are  hard  to  pull  apart.  The  original  hemispheres,  (2) 
Fig.  122,  were  14  inches  in  diameter  and  required  eight  horses  on  each 
side  to  pull  them  apart.  When  the  air  is  pumped  out  there  is  nothing 
inside  the  hemispheres  to  exert  pressure  outward  and  the  pressure 
of  the  atmosphere  holds  them  together. 

Show  this  with  (1),  Fig.  123.  Pull  the  handle  up  and  there  is  very 
little  air  inside  to  exert  pressure  outward.  Pull  out  the  end  stopper. 
Does  the  atmosphere  make  this  rather  difficult? 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      93 


(1)  Fig.  122 


(2)  Fig.  122.— The  First  Magdeburg  Hemisphere. 
Courtesy  of  The  MacMillan  Co. 


Show  it  also  with  (2).  Fill  the  quart  sealer  one  third  full  of  hot 
water,  put  on  the  rubber  ring  and  the  cover  but  do  not  seal,  place  the 
sealer  in  a  saucepan  of  salt  water,  heat  until  the  water  in  sealer  has 
boiled  for  one  or  two  minutes,  seal  and  stand  aside  until  quite  cold. 
Unseal  and  try  to  lift  the  cover.  Is  it  difficult? 

The  steam  formed  in  the  sealer  drives  out  the  air  and  when  the 
steam  condenses  there  is  a  vacuum  above  the  water  in  the  sealer.  There 
is  then  no  upward  pressure  under  the  cover  and  the  atmospheric 
pressure  on  top  makes  it  difficult  to  lift  the  cover. 


94      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  123.— Experi 
ments  Similar  to  That 
With  the  Magdeburg 
Hemispheres. 


Fig.   123.— Experiments    Similar  to  That  With 
the    Magdeburg    Hemispheres. 


When  the  plunger  is  raised  in  the 
tube,  (1),  Fig.  124,  the  atmospheric 
pressure  on  the  outside  forces  the 
sheet  of  rubber  in. 

Illustrate  this  also  by  means  of  (2). 
Fig.  124.  Suck  air  out  of  the  tube 
and  close  the  hose  with  a  clip.  Does 
the  atmosphere  force  the  rubber  in? 
Turn  the  rubber  in  all  directions.  Is 
the  pressure  of  the  atmosphere  equaj 
in  all  directions. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      95 


A  most  striking  me- 
thod of  showing  that 
the  atmosphere  exerts 
pressure  is  shown  in 
Fig.  125.  A  little  water 
is  placed  in  an  empty 
syrup  can  and  boiled 
until  the  steam  comes 
out  for  one  or  two  min- 
uts.  The  can  is  then 
closed  air  tight  and  in- 
verted in  a  dish  of  cold 
water.  In  a  short  time 
the  can  suddenly  col- 
lapses. 


M 


JL 


HH 
ft 


3fi 

ffi-m 


Fig.   124. — The   Atmosphere   Forces   the   Rubber   Sheet   In. 


Fig.   125. — The   Atmosphere    Crushes    the    Syrup    Can. 

The  reason   for  this   is   as   follows:  when   the   steam  has   driven   out 
the  air  there  is  nothing  left  in  the  can  but  water  and  steam,  and  when 


96      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


the  steam  condenses  in  the  closed  can,  there  is  nothing  in  the  space 
above  the  water,  to  exert  pressure  outward  and  the  can  must  stand  the 
whole  pressure  of  the  atmosphere.  If  it  is  not  strong  enough  to  do 
this,  it  collapses. 

Beg  or  buy  a  gallon  syrup  can  and  try  this  experiment,  it  will  cer- 
tainly surprise  you.  Be  sure  the  opening  is  covered  with  water  when 
you  invert  the  can  in  cold  water  because  the  water  will  help  to  make 
the  opening  air-tight. 

You  cannot  make  this  experiment  with  a  glass  bottle  because  the 
glass  is  strong  enough  to  support  the  atmosphere. 


HOW  ATMOSPHERIC  PRESSURE 
WAS   FIRST  MEASURED 


The  pressure  of  the  atmosphere  was  first 
measured  by  an  Italian  named  Torricelli  in 
1643,  with  apparatus  similar  to  that  shown  in 
Fig.  126.  His  experiment  was  essentially  as 
follows  :  A  glass  tube,  3  feet  long  and  closed 
at  one  end,  was  completely  filled  with  mercury 
(quicksilver)  to  expel  the  air;  the  open  end, 
closed  with  the  finger,  was  then  inverted  over 
a  dish  of  mercury,  and  the  finger  was  re- 
moved under  mercury. 


Fig.  126.— Torricelli's    Ex- 
periment. 
Courtesy  of  The  MacMillan  Co. 


He  found  that  some  of  the  mercury  came  out  of  the  tube  but  that 
a  column  remained  to  a  height  of  about  30  inches  above  the  surface 
of  the  mercury  in  the  dish. 

Since  no  air  enters  the  tube,  the  space  above  the  mercury  in  the 
tube  has  nothing  in  it,  that  is,  it  is  a  vacuum.  There  is,  therefore,  no 
pressure  downward  on  the  surface  of  the  mercury  in  the  tube,  and 
the  pressure  of  the  atmosphere  downward  on  the  surface  of  the  mer- 
cury in  the  dish  supports  the  column  of  mercury  in  the  tube. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      97 


HOW  THE  PRESSURE  OF  THE  ATMOSPHERE 
IS   MEASURED 


If  this  experiment  is  repeated  with  the  tube 
shown  in  Fig.  127,  the  top  of  the  mercury 
in  the  long  closed  tube  is  30  inches  above 
the  top  of  the  mercury  in  the  short  open  tube. 
Since,  as  you  will  show  shortly,  this  height 
is  independent  of  the  area  of  cross  section 
of  the  tube,  we  can  consider  this  to  be  just 
1  square  inch. 

The  pressure  of  the  atmosphere  on  1  square 
inch  at  A,  then,  supports  a  column  of  mercury 
BC  which  is  1  square  inch  in  area  and  30 


1  SQUARE 
INCH  AREA 


inches  high,  that  is,  it  supports  30  cubic  inches 


1  SQUARE 


Fig.    127.— Calculating    the 

Atmospheric   Pressure  on 

one  square  inch 


Courtesy  of 


c°- 


of  mercury. 

Now  1  cubic  inch  of  mercury  weighs  .49  tbs.  (nearly  y2  ft>.)  and  30 
cubic  inches  of  mercury  weigh  .49  x  30  =  14.7  ft>s.  The  pressure  of 
the  atmosphere  is  therefore  14.7  Ibs.  per  square  inch,  (nearly  IS  tbs.  per 
square  inch). 

It  is  a  very  astonishing  fact  that  the  atmosphere  exerts  14.7  Ibs. 
pressure  on  each  square  inch  of  every  thing  at  the  surface  of  the  earth. 
It  is  at  first  almost  unbelieveable,  but  you  have  already  made  exper- 
iments which  illustrate  this  pressure  and  you  will  make  others  as  you 
proceed. 

EXPERIMENT  No.  47 

To  measure  the  pressure  of  the  atmosphere. 

If  you  have  a  spring  balance  you  can  measure  the  pressure  of 
the  atmosphere  directly  with  the  apparatus,  Fig.  128,  as  follows. 

The  diameter  of  the  plunger  is  a  little  over  ^  inches  and  therefore 
its  area  is  3/10  square  inch.  If  then  the  pressure  of  the  atmosphere 
is  15  Ibs.  on  1  square  inch  it  is  IS  x  3/10  =  4^  Ibs.  on  3/10  square  inch. 

Soap  the  plunger  well  to  make  it  slippery,  shove  it  about  ^  way 
into  the  tube,  fill  the  remaining  %  of  the  tube  with  water,  and  insert 
a  solid  rubber  stopper  in  this  end,  (1).  Now  turn  the  tube  so  that  the 
plunger  handle  points  vertically  upward,  and  pour  a  little  water  in 
above  the  plunger  to  make  it  air-tight,  (2). 
A  —  I 


98      HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  128. — The  Atmosphere 

Exerts    the    Pressure    of 

15     Ibs.    per    square    inch, 

But  No  More 


Now  to  measure  the  pressure  of  the 
atmosphere,  attach  the  plunger  handle 
to  a  spring  balance,  hold  the  tube 
firmly  against  the  table,  and  ask  your 
partner  to  pull  upward  on  the  spring 
balance  while  you  observe  the  pull 
recorded  on  the  balance,  (3). 

Ask  him  to  lift  the  balance  slowly 
until  the  plunger  is  about  two  inches 
above  the  water,  then  ask  him  to 
allow  the  balance  to  go  back  slowly 
until  the  plunger  is  only  about  1  inch 
above  the  water.  While  he  is  doing 
this  you  must  read  the  average  pull 
on  the  balance. 

Do  you  find  this  average  pull  to  be 
72  ozs.  or  4^  Ibs? 

Note:  While  your  partner  is  raising 
the  plunger,  the  friction  of  the  plunger 
against  the  sides  of  the  tube  is  work- 
ing against  the  balance  and  the  pull 
will  be  over  Al/2  Ibs;  but  while  he  is 
lowering  the  plunger,  the  friction  will 
be  working  with  the  balance  and  the 
pull  will  be  less  than  4^  Ibs.  The 
average  will  be  about  4>£  Ibs. 

You  have  shown  here  that  the  pres- 
sure of  the  atmosphere  is  4Vj  Ibs.  on 
3/10  sq.  in.  or  4^  x  10/3  =  15  Ibs.  on 
1  square  inch. 

THE  BAROMETER 

The  barometer,  Fig.  129,  is  the  chief 
instrument  used  by  the  Weather  Bu- 
reau in  forecasting  the  weather.  It 
Is  an  apparatus  similar  to  that  used 
by  Torricelli  in  his  experiment.  The 
pressure  of  the  atmosphere  on  the 
mercury  in  the  open  tube  or  cup  sup- 
ports a  column  of  mercury  about 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING      99 


1  2 

Fig.     129. — Barometers 

l-Courtesv  of  the 

MacMillan  Co. 

2-From  the 

"Ontario  High  School 

Physics' ' .    By  Perm  ission  of 

the  Publishers 


tight  metal  box  from 
which  the  air  is  ex- 
exhausted.  The  atmos- 
pheric pressure  would 
force  together  the  top 
and  bottom  of  this 
box  if  they  were  not 
kept  apart  by  the 
strong  spring  shown 


30  in.  high  in  the  long  closed  tube. 
The  pressure  of  the  atmosphere  varies 
from  hour  to  hour  and  the  height  of 
the  mercury  column  varies  with  it. 
Weather  forecasts  are  based  on  this 
variation. 

It   has   been    found   that   when   the 
mercury  falls  much  below  30  in.,  be- 
cause the  atmospheric  pressure  is  low, 
bad  weather   may   be    expected;   and 
when   the   mercury   rises   much  above 
30    inches,    because    the    atmospheric 
pressure   is   high,  good  weather  may 
be  expected.    The  extreme  variations  are  from 
about  29  in.  to  31  in. 

The  barometer  (2)  is  the  type  used  on  ships, 
and  when  a  sailor  says  "the  glass  is  falling" 
he  means  that  the  mercury  in  the  glass  tube 
is  sinking  below  30  in.  and  that  bad  weather 
is  to  be  expected;  when  he  says  "the  glass  is 
rising,"  he  means  that  the  mercury  is  rising 
above  30  in.  and  that  fine  weather  is  to  be 
expected. 

Another  type  of  barometer  is  shown  in  Fig. 
130.  It  is  called  an  aneroid  barometer  because 
it  contains  no  liquid.  It  has  a  flat,  round,  air- 


Fig.  130 

Fig.   130. — Aneroid   Barometer 
Courtesy  vf  The  liltclltilan  Co. 


100    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


above  the  box.  If  the  atmospheric  pressure  increases,  the  spring  is 
forced  down;  if  the  pressure  decreases,  the  spring  rises.  The  move- 
ments are  very  small,  but  they  are  magnified  by  levers  and  are  com- 
municated to  the  pointer  by  means  of  a  rack  and  pinion. 

HOW  AIRMEN  KNOW  THEIR  ALTITUDE 
THE  ALTITUDE  GAUGE 


sum  e*rru  tuna 


Air  Zones  of  Modern  Battle  (1918) 


The  air  zones  of  a 
modern  battle  are  illus- 
trated in  Fig.  131  and 
the  altitude  guage  by 
means  of  which  the  air- 
men know  their  height 
is  shown  in  Fig.  132. 
This  altitude  gauge  is 
a  recording  aneroid 
barometer  called  a  bar- 
ograph. It  records  the 
height  of  the  airplane 
in  feet  and  is  suspend- 
ed free  of  the  airplane 
by  four  elastic  straps 
which  protect  it,  to 
some  extent,  from  the 
vibration  of  the  ma- 
chine. 

The  construction  of 
the  barograph  is  as  fol- 
lows. It  has  five  or  six 
flat  metal  boxes,  ex- 
hausted of  air,  similar 
to  the  box  in  the  or- 
dinary aneroid.  These 
boxes  are  expanded  by 
a  strong  spring,  as  the 
height  increases,  and 
this  movement  is  com- 
municated to  the  long 


Fig.   131.— Air  Zones 

Courtesy  of  "The  World's  Work", 
Garden  City,  N.  Y. 

pointer.  On  the  end  of  the  pointer  there  is  a  pen,  with  a  supply  of  ink, 
which  bears  against  a  sheet  of  paper  on  a  drum  revolved  by  clockwork. 
The  pen  makes  a  continuous  record  on  the  paper  of  the  height  in  feet. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    101 


I          Mercury 
Barometer 


"   :  tfig!    ij2.*-The'  'Altitude    Gauge    or 


Fig.    133.— Water    Barometer 


THE  WATER  BAROMETER 

Any  liquid  can  be  used  in  a  bar- 
ometer but  liquids  lighter  than  mer- 
cury require  longer  tubes.  This  is 
true  of  the  water  barometer.  Mer- 
cury is  13.6  times  as  heavy  as  water 
and  since  the  atmosphere  supports 
a  column  of  mercury  30  in.  high 
it  will  support  a  column  of  water 
13.6  x  30  =  408  in.  high,  that  is,  a 
column  408/12  =  34  feet  high. 

Otto  von  Guericke,  the  inventor 
of  the  Magdeburg  hemispheres, 
made  a  water  barometer  in  1650, 
and  had  it  so  arranged  that  the  top 
of  the  tube  stuck  up  through  the 
roof  of  his  house.  He  had  a  small 
wooden  figure  floating  on  the  water 
in  the  tube  and  in  fine  weather, 
when  the  water  column  rose,  the 
figure  rose  above  the  roof,  but  in 
bad  weather  the  figure  retired  from 
sight.  This  frightened  and  mysti- 
fied his  neighbors  very  much  and 
they  accused  him  of  being  in  league 
with  the  evil  one. 


102    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


EXPERIMENT  No.  48 

To  show  that  the  vertical  height  to  which  the  atmosphere  will  lift 
water  in  a  tube  is  independent  of  the  length  or  slant  of  the  tube. 

Make  the  experiments  (1),  (2)  and  (3), 
Fig.  134.  Suck  air  out  through  the  upper 
coupling  on  the  tee  and  close  the  clip. 

Is  the  vertical  height  of  the  water  in 
one  tube  above  the  water  in  the  tum- 
bler always  the  same  as  that  in  the 
other? 

Make  experiments  of  ypur  own. 


Fig.   134. — The  Height  is  independent  of  the 
Length  and   Slant   of  the  Tube 

EXPERIMENT  No.  49 

To   show   that   the   height   to   which  the 
atmosphere  will  lift  water  in  a  tube  is  inde- 
pendent of  the  size  or  shape  of  the  tube 
and  of  the  water  sur- 
face outside  the  tube. 

Make  the  experiments 
(1),  (2),  (3)  and  (4)  Fig. 
135.  Is  the  height  of  the 
water  always  the  same 
in  the  two  tubes? 

Make  experiments  of 
your  own. 


Fig.   135 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING     103 


EXPERIMENT  No.  50 


Fig.    135.— The   Height 

is    independent     of    the 

size     or     shape     of     the 

Tube  and  of  the  Water     To  show  that  the  atmosphere 

Surface  outside  the  Tube  lifts  heavy  salt  water  to  a 
less  height,  and  light  gasoline 
to  a  greater  height,  than  it 
lifts  fresh  water. 
Make  the  experiments  illus- 
trated in  Fig.  136. 


EXPERIMENT  No.  51 

To  show  that  the  atmosphere 
will  lift  weights. 
Make  the  experiments  illus- 
trated in  Fig.  137. 


Fig.  136. — Salt  Water  is  raised  to  a  less' 
height  than  Fresh  Water,  and  Gasoline  to  a 
greater  height. 


Fig.    137.— ^howing   that   the  At- 
mosphere will  lift  weight. 


104    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


ini 


Fig.  138. — Showing 
that  the  Atmosphere 
•will  lift  15  tt>s.  per 
sq.  in.  but  no  more. 


EXPERIMENT  No.  52 

To  show  that  the  atmosphere  will  lift 
15  Ibs.  per  sq.  in.  but  no  more. 

The  plungers  have  an  area  of  3/10 
sq.  in.  If  then,  the  atmosphere  will 
lift  15  Ibs.  on  1  sq.  in.,  it  will  lift  3/10 
x  15  =  V/2  Ibs.  on  3/10  sq.  in. 

Soap  the  plungers,  have  water  be- 
tween them  but  no  air,  pour  an  inch 
of  water  above  the  upper  plunger  to 
make  it  air-tight,  attach  a  pail  weigh- 
ing less  than  4^2  Ibs.  to  the  lower 
plunger,  Fig.  138  and  raise  the  upper 
plunger.  Does  the  atmosphere  lift 
the  lower  plunger  and  weight? 

Add  water  to  the  pail  until  the  to- 
tal weight  is  tyz  Ibs.  and  raise  the 
upper  plunger.  Do  you  find  that  the 
atmosphere  does  not  lift  the  lower 
plunger?  It  does  not  do  so  because 
the  atmospheric  pressure  on  3/10  sq. 
in.  cannot  lift  4^  Ibs.  and  also  OTCF- 
come  the  friction. 

Hold  the  upper  plunger  and  lift  the 
tube.  Does  the  atmosphere  now  lift 
4^  Ibs.  weight?  It  does  so  because 
the  friction  helps  it  in  this  case. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    105 

Repeat  with  the  water  and  pail  weighing  6  Ibs.  Do  you  find  that 
the  atmospheric  pressure  on  3/10  sq.  in.  will  not  lift  6  Ibs.  even  with 
the  help  of  the  friction. 

You  have  shown  here  roughly  that  the  atmospheric  pressure  on  3/10 
sq.  in.  will  lift  4^  Ibs.  but  no  more.  This  shows  that  the  atmospheric 
pressure  on  1  sq.  in.  will  lift  4.5  x  10/3  =  15  Ibs.  but  no  more. 

Make  your  own  experiments. 


AIR-LIFT  PUMPS 

The  air-lift  pump,  Fig.  139, 
is  operated  by  compressed  air. 
It  consists  of  two  pipes  one 
inside  the  other,  both  open  at 
the  bottom  and  without  val- 

Fig.   139.-An  Air-Lift  Pump  ves-     Th«    P"mP    w    at    least 
half-submerged,    that    is,   the 

bottom  is  at  least  as  far  below  the  surface  of  the  water 
in  the  well  as  the  top  is  above  it. 

The  air  which  is  compressed  in  the  storage  tank  passes 
into  the  outer  pipe  of  the  pump,  forces  the  water  down 
to  the  bottom  of  the  inner  pipe,  and  forces  the  water  in 
the  inner  pipe  up  into  the  tank.  After  the  first  lot  of 
water  has  been  forced  out  of  the  inner  pipe  the  pump 
settles  down  to  its  regular  operation  which  is  as  follows. 
Compressed  air  from  the  outer  pipe  enters  the  inner  pipe, 
the  pressure  in  the  outer  pipe  is  thereby  lowered  and  the 
water  rises  in  the  outer  pipe  above  the  bottom  of  the 
inner  pipe,  more  compressed  air  comes  from  the  tank  and 
forces  the  water  down  in  the  outer  pipe  but  up  in  the 
inner  pipe.  This  operation  takes  place  over  and  over  again  rapidly, 
and  alternate  layers  of  air  and  water  are  forced  up  the  inner  pipe  as 
shown  in  Fig.  139.  The  water  thus  flows  from  the  inner  pipe  into  the 
tank  in  spurts  as  you  will  show  in  your  next  experiment. 

Another  form   of  air-lift  pump   is   illustrated  in  Fig.  140.    Here   the 
air  enters  through  the  inner  pipe  and  the  mixture  of  water  and  air  is 


106    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


forced  out  through  the  outer  pipe.  The  water  comes  out  as  a  continuous 
heavy  spray  because  the  air  is  mixed  with  the  water  in  bubbles  rather 
than  in  layers. 

These  are  called  air-lift  pumps  but  the  water  is  not  raised  by  the 
air  pressure.  It  is  raised  by  the  weight  of  the  water  in  the  well  out- 
side the  pump,  because  the  water  rising  in  the  pump  is  really  a  mixture 
of  air  and  water  and  is  lighter  than  a  water  column  of  the  same  height. 


You  can  illustrate  this  by  means  of  ex- 
periments shown  in  Fig.  141.  In  (1) 
both  sides  of  the  U  tube  are  filled  with 
water  and  you  know  from  your  experi- 
ments that  the  water  will  be  at  the 
same  level  in  both  sides.  In  (II)  one 
side  is  filled  with  kerosene  oil  which  is 
only  8/10  as  heavy  as  water,  and  you 
know  that  a  column  of  water  8  in.  high 
will  support  a  column  of  oil  10  in  high. 
Similarly  in  (III)  a  depth  of  water  of 
8  inches  will  support  a  column  of  oil  10 
inches  high.  If  now  the  oil  in  (III)  were 
replaced  by  a  mixture  of  air  ond  water 
which  was  only  1/2  as  heavy  as  water, 
you  can  see  that  the  8  inch  depth  of 
water  would  support  a  column  of  the 
mixture  16  inches  high,  and  so  on. 

The  bottom  of  the  air-lift  pump  is  al- 
ways placed  at  least  as  far  below  the  sur- 


compressed 
air      «»s 


Fig.   141. — A  Column  of  Water  sup- 
ports a  longer  column  of  a   Light  Oil. 
Courtesy  of  the  MacMillan  Co. 


Fig.    140. — Another   type    of   Air-Lift 
Pump 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    107 


face  of  the  water  as  the  top  is  above,  and  the  water  outside  the  pump 
lifts  the  lighter  mixture  of  air  and  water  to  the  top.  You  will  illustrate 
this  in  the  next  experiment. 

EXPERIMENT  No.  53 

To  make  and  operate  two  air-lift  pumps. 

Make  an  air-lift  pump.  (1)  Fig.  142.  Use  a 
quart  sealer  to  represent  the  well,  fill  it  to 
the  top  with  water,  and  insert  the  air-lift 
pump  until  it  is  half  submerged,  that  is,  until 
the  water  in  the  sealer  is  at  a  point  half  way 
between  the  bottom  of  the  wide  tube  and  the 
top  of  the  elbow  of  the  discharge  pipe. 

Force  air  in 
through  the  hose 
and  observe  what 
takes  place  near 
the  bottom  of  the 
pump. 

Do  you  observe 
that  the  water 
level  in  the  pump 
moves  alternately 
down  below  the 
end  of  the  dis- 
charge pipe  and 
then  up  above  it, 
and  that  altern- 
ately water  and 
air  are  forced  up 
the  discharge 
pipe? 

Do  you  observe 
further  that  when 
you  force  air  in 
at  just  the  right 
rate  the  pump 
works  steadily 
and  the  water 
1  2  comes  up  the  dis- 

Fig.    142. — Illustrating   the   working   of  ... 

two  different  Air-Lift  Pumps.  charge       pipe       in 


108    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

spurts   at  regular  intervals. 

In  the  other  type  of  air-lift  pump  the  compressed  air  passes  down 
the  inside  pipe  and  the  mixed  air  and  water  move  up  the  other  pipe. 

Make  a  pump  of  this  kind,  (2)  Fig.  142  and  blow  air  in  through  the 
inside  pipe. 

Do  you   find  that  air  and  water  are   forced  up   over   the   top   of   the 
outside   pipe? 

Repeat  the  experiment  with  the  pump  deeper  in  the  water. 

Do  you  find  that  it  works  better  the  deeper  it  is  in  the  water? 

LAWS  WHICH  APPLY  TO  GASES 
PASCAL'S  LAW 

In  the  remaining  pages  of  this  book  you  will  study  three  laws  which 
apply  to  gases  and  you  will  illustrate  many  practical  applications  of 
these  laws.  They  are  Pascal's  law,  Archimedes'  law,  and  Boyle's  law. 
You  will  begin  with  Pascal's  law. 

You  learned  on  pages  49,  50  and  51,  Pascal's  law  which  states  one  pro- 
perty of  liquids;  namely,  pressure  exerted  on  a  liquid  is  transmitted 
by  the  liquid  equally  and  undiminished  in  all  directions.  This  law  also 
states  a  property  of  gases  as  follows  :  pressure  applied  to  a  gas  is  trans- 
mitted by  the  gas  equally  and  undiminished  in  all  directions. 

You  are  very  familiar  with  one  application  of  this  law,  namely  in  the 
pneumatic  tire.  The  air  in  a  bicycle  or  automobile  tire  exerts  pressure 
outward  equally  at  every  part  of  the  tire. 

EXPERIMENT  No.  54 

To  illustrate  Pascal's  law  as  it  applies  to  gases. 

Shove  the  plunger  in  (1)  Fig.  143,  down,  and  feel  the  air  at  the  nozzles. 
Are  the  pressures  equal? 

Blow  a  soap  bubble  (2).  Is  it  a  perfect  sphere?  This  shows  that 
the  air  exerts  pressure  equally  in  all  directions  against  the  inside  of 
the  bubble. 

Make  a  three  legged  siphon  filled  with  air  (3),  place  two  legs  in 
tumblers  of  water,  place  the  third  leg  in  the  wide  tube  partly  filled 
with  water,  and  raise  and  lower  the  wide  tube. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING     109 


Fig.    143. — Showing   that 

Air  transmits   Pressure 

Equally     and     Undimin- 

ished    in    all    directions. 


The  water  in  the  wide  tube  exerts  pressure  on  the  air  in  the  third 
leg.  Is  this  pressure  exerted  equally  and  undiminUhed  by  the  air,  that 
is,  is  the  water  level  in  the  three  legs  always  at  the  same  distance 
below  the  water  outside? 

Repeat  this  with  the  apparatus   (4).    Is  the  result  the  same? 

You  have  here  proved  Pascal's  law,  namely  that  a  gas  transmits 
pressure  equally  and  undiminished  in  all  directions. 


110    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


BALLOONS  AND  THE  BUOYANT  FORCE  OF  AIR 
The  Law  of  Archimedes  applied  to  Gases 

Balloons  float  in  air  and  this  fact  is  due  to  a  property  of  air  which 
is  expressed  by  the  law  of  Archimedes. 

You  have  already  made  experiments  on  this  law  with  liquids  and  you 
have  shown  that  the  buoyant  force  of  a  liquid  on  a  body  is  equal  to  the 
weight  of  the  liquid  displaced  by  the  body.  This  is  the  law  of  Archi- 
medes as  it  applies  to  liquids. 

The  law  of  Archimedes  in  regard  to  gases  is  :  the  buoyant  force  of  a 
gas  on  a  body  is  equal  to  the  weight  of  the  gas  displaced  by  the  body. 


Fig.   144. — The  Buoyant  Force  on  the  Balloon  is  Equal 

to  the  Weight   of  Air  displaced  by  the  Balloon 

Courtesy  of  "The  Scientific  American" 

How  the  Total  Lift  of  a  Balloon  is  Calculated 

The  weight  of  air  is  about  \Y$  ounces  per  cubic  foot  at  ordinary  tem- 
peratures and  at  the  surface  of  the  earth.  If  then  a  balloon  displaces 
1,000,000  cubic  feet  of  air,  its  total  lift  or  buoyancy  is  5/4  x  1,000,000  = 
1,250,000  ounces  =  1,250,000/16  Ibs.  =  78,125  ibs.  and  so  on.  The  useful 
load  a  balloon  can  lift  is  its  total  lift  minus  the  weight  of  the  envelope, 
of  the  gas  in  the  envelope,  of  the  cars,  of  the  engines,  and  of  the  fuel. 

In  Fig.  145  we  show  the  relative  strengths  in  dirigible  balloons  of 
Germany,  France  and  Great  Britain  at  the  beginning  of  the  war.  Britain 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    111 

and  France  built  many  dirigibles  during  the  war  and  one  of  the  latest 
built  by  Britain  displaces  1,600,000  cubic  feet  of  air.  Its  total  lift  there- 
fore is  1,600,000/16  x  5/4  =  125,000  Ibs. 

The  balloon  is  filled  with  hydrogen  which  weighs  about  1/14  as  much 
as  air,  and  therefore  1/14  of  the  total  lift  is  used  up  in  lifting  the 
hydrogen  gas.  The  weight  of  the  hydrogen  is  125,000/14  =  8928  Ibs. 


Fig.    145. — Comparative  Zeppelin   Strength   of   Germany,    France 
Great   Britain  at  the   Outbreak  of  the   Great  World  War. 

On  the  left,  thirteen  German  ships  in  commission  and  four  (in  white)   building. 
On  the  right,  above,  one  French  ship  built  and  two  building. 
On  the  right,  below,  two  British  ships  building. 

Courtesy  of  The  Scientific  American 


Hydrogen  gas  has  been  used  in  balloons  because  it  is  the  lightest 
gas  known.  It  has  one  great  drawback,  however,  in  that  it  burns  very 
readily.  There  is  another  gas  called  helium  which  is  twice  as  heavy  as 
hydrogen  but  which  has  the  great  advantage  that  it  does  not  burn. 

Before  the  war  helium  was  very  expensive  but  during  the  war  it  was 
found  that  the  helium  which  occurs  in  some  of  the  natural  gases  of  the 
United  States  could  be  separated  at  a  reasonable  cost.  It  is  expected 
that  the  dirigibles  of  the  future  will  be  filled  with  helium,  and  since  it 
does  not  burn,  it  will  be  possible  to  put  the  engines  in  a  room  inside 
the  balloon  as  shown  in  Fig.  146. 


112    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  146. — Conception  of  the  Passenger-Carrying  Dirigible  of 
the  Near  Future  making  use  of  Helium  Gas 
Courtesy  of  the  Scientific  A  merican 


Although  helium  is  twice  as  heavy  as  hydrogen  its  lifting  power  is 
only  1/13  less  because  the  lift  of  a  balloon  depends  primarily  on  the 
weight  of  air  displaced.  You  can  show  this  as  follows : 

If  a  balloon  displaces  140,000  Ibs.  of  air  and  it  is  filled  with  hydrogen, 
it  holds  140,000/14  =  10,000  Ibs.  of  hydrogen,  since  hydrogen  weighs  1/14 
as  much  as  air. 

If  the  balloon  is  filled  with  helium  it  holds  140,000/7  =  20,000  Ibs.  of 
helium,  since  helium  weighs  1/7  as  much  as  air. 

The  lift  minus  the  weight  of  hydrogen  =  140,000  —  10,000  =  130,000  Ibs. 

The  lift  minus  the  weight  of  helium  =  140,000  —  20,000  =  120,000  Ibs. 

That  is,  the  lift  with  helium  is  only  1/13  less. 

EXPERIMENT  No.  55 

To  illustrate  the  buoyant  force  of  air. 
Blow  a  soap  bubble  with  illuminating  gas  (1)  Fig.  147. 
Does  the  bubble  rise? 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    113 


«HYE 


Fig.    147.— Filling    a    Bubble   and    a    Balloon    with    Illuminating    Gas 

Blow  up  a  balloon  with  illuminating  gas  by  means  of  the  force  pump 
(2)  Fig.  147.    Does  the  balloon  rise? 

The  bubble  and  balloon  rise  because  they  displace  a  greater  weight 
of  air  than  their  own  weight  plus  the  weight  of  the  gas  in  them. 


EXPERIMENT  No.  56 

To  illustrate  the  buoyant  force  of  air  by  means  of  a  balloon  filled 
with  hydrogen. 
A  — 8 


114    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


If  the  metal  zinc  is  placed  in  an  acid,  the  metal  is  dissolved  by  the 
acid  and  hydrogen  gas  is  produced.  You  can  make  hydrogen  gas  and 
fill  the  large  balloon  with  it  as  follows. 

Purchase  at  a  drug  store  2  ounces  of  strong  hydrochloric  acid  (also 
called  muriatic  acid)  which  should  cost  about  5  or  10  cents ;  also  pur- 
chase at  an  electrical  shop  a  zinc  rod  for  a  Leclanche  battery,  which 
will  also  cost  about  5  or  10  cents,  or  purchase  two  zinc  strips. 

Pour  the  acid  into  the  bottle  and 
add  an  equal  volume  of  water.  This 
dilutes  the  acid  and  slows  up  the 
production  of  the  hydrogen.  If  the 
hydrogen  is  produced  too  fast  it 
will  bubble  acid  up  into  the  balloon. 

Now  to  make  hydrogen  and  to 
fill  the  balloon,  proceed  as  follows  : 
Arrange  the  bottle  as  shown  in 
Fig.  148  and  attach  the  large  bal- 
loon to  the  elbow  by  means  of 
a  short  piece  (about  \Y2  in.)  of  a 
stretched  rubber  band.  When  you 
have  done  this  place  the  zinc  rod 
or  zinc  strips  gently  in  the  bottle, 
insert  the  stopper  at  once,  and  al- 
low the  hydrogen  to  fill  the  balloon.  It  will  take  about  5  minutes  to 
fill  the  large  balloon  completely. 

When  the  balloon  floats  well  in  the  air,  slip  it  off  the  elbow  with  its 
stretched  rubber  band.  The  band  will  contract  and  close  the  balloon. 

Now  release  the  balloon.  Do  you  find  that  it  floats  up  to  the  ceiling? 
Precautions.  Be  very  careful  not  to  get  any  of  the  acid  on  your  hands 
or  clothes.  It  will  burn  very  bad  holes  if  it  does. 

When  you  are  through  empty  out  the  liquid  left  in  the  bottle,  as  it 
is  of  no  further  use,  and  rinse  the  bottle  and  rod  very  thoroughly  with 
water. 

You  must  not  use  the  zinc  in  small  pieces  because  it  produces  the 
hydrogen  too  fast  and  makes  the  acid  bubble  up  into  the  balloon.  Use 
the  zinc  in  the  shape  of  a  rod  or  strips. 


Fig.    148. — Filling   a   Balloon   with 
Hydrogen 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    115 


EXPERIMENT  No.  57 

To  shoot  down  a  balloon. 

We  show  in  Fig.  149  three  views  of  a  balloon  shot  down  by  means 
of  incendiary  bullets.  These  bullets  set  the  hydrogen  on  fire,  the  en- 
velope burns,  and  the  car  and  machinery  fall  to  the  ground. 


r  * 


Fig.  149. — Three  Phases  of  a  Successful  Attack  on  an 
Obseravtion    Balloon 

1  —  Immediately  after  the  "hit"  has  been  scored.     Note  the  aeroplane  and  balloon. 

2  —  Balloon  enveloped  in  flames  is  fast  reduced  to  a  shapeless  mass. 

3  —  Wreckage  of  the  observation  balloon  falling  to  earth,  with  a  smoke  trail  in  its 

wake. 

Courtesy  of  the  Scientific  American 

A  toy  balloon  filled  with  hydrogen  as  in  the  last  experiment  floats 
up  to  the  ceiling.  It  will  come  down  by  itself  in  a  few  hours  because 
the  hydrogen  gradually  passes  out  through  the  rubber. 

If  you  are  in  a  hurry  to  get  the  balloon  down,  and  if  you  have  an 
air  riflle,  you  can  shoot  a  hole  through  the  balloon :  the  hydrogen  will 
then  escape  and  the  balloon  will  fall  at  once.  This  method,  however, 
spoils  the  balloon. 


116    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


You  can  shoot  the  balloon  down  with  a  syringe 
without  destroying  it  as  shown  in  Fig.  150.  The 
water  on  the  balloon  will  make  its  weight  greater 
than  the  buoyancy  of  the  air  displaced  by  the  bal- 
loon and  this  will  bring  it  down. 

If  you  let  the  water  evaporate,  the  balloon  will 
rise  again  because  it  again  becomes  lighter  than  the 
air  it  displaces.  You  can  then  shoot  it  down  again 
with  water. 

EXPERIMENT  No.  58 

To  illustrate  the  buoyant  force  of  a  gas  heavier 
than  air  by  means  of  a  soap  bubble  filled  with  air. 

Purchase  at  a  drug  store  one  ounce  of  ether  and 
pour  it  into  an  empty  12  qt.  pail,  cover  the  pail 
with  a  newspaper  and  allow  it  to  stand  for  about 
10  minutes. 

The  ether  will  evaporate  and  produce  ether  gas. 
This  being  heavier  than  air  will  remain  in  the  bot- 
Fig     150— Shooting    tom  of  the  pail  an<*  *orce  the  lighter  air  out  at  the 

Down    a     Small    Balloontop. 


Now  dip  the  end  of  the  wide  tube  in  the  soap 
suds  and  shake  off  the  excess  soapy  water.  Blow 
a  large  bubble  and  detach  it  about  6  in.  above 
the  bottom  of  the  pail. 

Do  you  find  that  the  soap  bubble  filled  with  air 
floats  on  the  heavy  ether  gas? 

The  buoyant  force  of  the  ether  gas  is  the 
weight  of  this  gas  displaced  by  the  bubble.  This 
buoyant  force  is  sufficient  to  support  the  soap 
bubble  film  and  the  air  inside  of  it. 


Fig.  151.— Illustrating 
the  Buoyant  Effect  of 
a  Heavy  Gas. 


1 

Fig. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    117 

COMPRESSED  AND  EXPANDED  GASES 

BOYLE'S   LAW 


You  will  now  illustrate 
Boyle's  law  and  then  make 
a  number  of  appliances 
which  make  use  of  this 
law,  namely,  the  air  brake, 
flame  thrower,  fire  extin- 
guisher, air  pump,  bicycle 
pump,  sand  blast,  pneu- 
matic paint  brush,  diving 
bell,  pneumatic  caisson, 
and  submarine  air  supply. 

Boyle's  law  is  :  The  vol- 
ume of  a.  gas  varies  inver- 
sely as  the  pressure  on  it. 

This  is  illustrated  in  Fig. 
152.  In  (1)  the  tube  is 
full  of  air  and  the  pressure 
on  the  air  is  one  atmos- 
phere because  the  tube  is 
open  to  the  atmosphere. 
In  (2)  the  pressure  on  the 
air  is  2  atmospheres  and 
the  volume  of  the  air  is 
1/2  what  it  was  in  (1).  In 
(3)  the  pressure  on  the 
air  is  3  atmospheres  and 
1/3  what  is  was  in  (1)  and  so  on. 


152.- 


3456 

-The  Volume  of  a   Gas  Varies   Inversely 
as  a  Presure  on  it 


the  volume  of  the  air 


IS 


In  (4)  the  air  in  the  tube  below  the  plunger  is  under  1  atmosphere 
pressure  because  the  tube  is  open  to  the  atmosphere.  In  (5)  the  tube 
is  closed,  the  plunger  is  raised  until  the  pressure  on  the  air  is  1/2  at- 
mosphere and  its  volume  is  two  times  what  it  was  in  (4).  In  (6)  the 
plunger  is  raised  until  the  pressure  on  the  air .  in  only  1/3  and  its 
volume  is  three  times  what  it  was  in  (4). 


These  illustrate  Boyle's  law. 


118    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Boyle's  law  is  usually  illustrated  by  means  of  the 
apparatus  shown  in  Fig.  153.  The  glass  tube  A  is  closed 
at  the  top  and  is  partly  filled  with  air,  the  second  glass 
tube  B  is  open  at  the  top,  and  the  two  tubes  are  con- 
nected by  a  rubber  tube  filled  with  mercury. 

The  mercury  surfaces  at  the  beginning  are  at  the 
same  level,  (1)  Fig.  154,  and  since  the  pressure  on  the 
mercury  surface  in  B  is  1  atmosphere,  the  pressure 
on  the  air  in  A  is  also  1  atmosphere. 

If  now  B  is  raised  until  its  mercury 
surface  is  30  in.  above  that  in  A,  the 
air  in  A  is  under  2  atmospheres  pres- 
sure and  it  is  compressed  to  1/2  its 
first  volume,  (2). 

If  B  is  raised  until 
its  mercury  surface  is 
60  in.  above  that  in  A, 


Fig.    153. — Apparatus 

used    to    Illustrate 

Boyle's   Law 

Courtesy    of 

The  MacMMan  C*. 


the  air  in  A  is  under  3 
atmospheres  pressure  and 
it  is  compressed  to  1/3  its 
first  volume  (3),  and  so  on. 
If  on  the  other  hand,  B 
is  lowered,  (5),  until  its 
mercury  surface  is  15  in. 


2  3 

Fig.   154. — Illustrating  Boyle's  Law 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    119 


Vol.  2 


15' 


Vol.  3 


Illustrating  Boyle's   Law 


below  that  in  A,  the  air 
in  A  is  under  a  pressure 
of  only  1/2  atmosphere 
and  it  expands  until  its 
volume  is  2  times  its  vol- 
ume in  (4). 

If  B  is  lowered  (6)  until 
its  mercury  surface  is  20 
in.  below  that  in  A,  the  air 
in  A  is  under  a  pressure 
of  only  1/3  atmosphere 
and  it  expands  until  its 
volume  is  3  times  its  vol- 
ume in  (4),  and  so  on. 

Note:  A  column  of  mer- 
cury 30  inches  high  exerts 
a  pressure  equal  to  that 
of  one  atmosphere.  Sim- 
ilarly 15  in.  =  1/2  atmos- 
phere and  10  in.  =  1/3 
atmosphere. 


EXPERIMENT  No.  59 

To  illustrate  Boyle's  law. 

If  you  have  a  spring  balance  you  can  prove  Boyle's  law  as  follows : 
Use  the  apparatus  (1)  Fig.  155  and  compress  the  air  to  one  half  its 
volume  as  in  (2).  Is  the  average  pull  on  the  balance  4^  Ibs.? 

Note:  Friction  opposes  the  plunger  when  it  is  moving  in,  but  it 
helps  the  plunger  to  remain  in.  You  will  find  that  it  takes  more  than 
4*/2  Ibs.  to  compress  the  gas,  but  less  than  4^  Ibs.  to  hold  it  after  it 
is  compressed,  the  average  is  4l/2  Ibs. 


120    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


The  area  of  the  plunger  is 
3/10  sq.  in.,  therefore  the 
pressure  per  square  inch  is 
4.5  x  10/3  =  15  Ibs.  or  1  at- 
mosphere, but  the  air  on  the 
outside  exerts  a  pressure  of 
1  atmosphere  on  the  plunger, 
therefore  the  total  pressure 
the  plunger  exerts  on  the  air 
in  the  tube  is  1  +  1  =  2  at- 
mospheres. 

You  have  shown  here  that 
when  you  double  the  pressure 
on  a  gas  you  compress  the 
gas  to  one  half  its  first  vol- 
ume. 

To  show  that  when  you 
halve  the  pressure  on  a  gas 
its  volume  doubles,  use  the 
apparatus  (3)  Fig.  155. 

Start  with  a  distance  of  2 
inches  between  the  plungers, 
(3)  then  pull  up  the  spring 
balance  until  the  distance  is 
4  inches,  (4).  Is  the  average 
pull  on  the  balance  2%  Ibs.? 

A  pull  of  2%  Ibs.  on  3/10 
sq.  in.  is  2.25  x  10/3  =  7.5  Ibs. 
per  sq.  in.  or  y2  atmosphere. 
Since  the  pull  of  the  balance 
is  only  */2  atmosphere,  the  air 
in  the  tube  must  be  exerting 
the  other  */2  atmosphere. 

Fig.   155.— Double  the  Pressure   on  Air  and  you          You   have   shown  here   that 

Half  the  Volume.    Half  the  Pressure  and  you      when  the  pressure  on  air  is 

Double    the    Volume.  halyed    {^    yolume    increases 

to  double  what  it  was  at  first. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING     121 


THE  AIR  BRAKE 


Fig.    156.— Air    Brakes    for   Trains 
From  the  "Ontario  High  School  Physics",  By  Permission  of  the  Publishers 


One  of  the  commonest  applications  of  compressed  air  is  in  the  air 
brakes  on  trains.  The  air  compressor  A,  on  the  side  of  the  engine 
boiler,  is  operated  by  steam  from  the  boiler.  It  compresses  air  in  the 
large  tank  B,  on  the  locomotive,  and  this  compressed  air  is  carried 
through  the  train  pipe  under  the  cars  to  the  air  brake  under  each  car. 
The  air  brake  on  each  car  consists  of  a  triple  valve  F,  an  air  tank  E 
and  a  cylinder  C  containing  a  piston  P.  The  brake  beam  is  attached 
to  D. 

The  operation  of  the  air  brakes  is  as  follows :  Air  is  pumped  into  the 
locomotive  tank  B  until  its  pressure  is  about  75  tbs.  per  sq.  in.  This 
compressed  air  moves  through  the  train  pipe,  through  the  triple  valve 
F,  and  into  the  car  tanks  E. 

When  the  train  is  running,  the  pressure  in  each  car  tank  E  is  equal 
to  that  in  the  locomotive  tank  B ;  but  there  is  no  air  in  the  cylinder  C 
and  the  brakes  are  "off",  because  the  spring  holds  the  piston  P  in  the 
position  shown. 

When  the  engineer  puts  "on"  the  brakes,  he  turns  a  lever  which  closes 
the  valve  between  B  and  the  train  pipe,  and  which  at  the  same  time,  lets 
the  air  out  of  the  train  pipe.  When  the  air  pressure  in  the  train  pipe 


122    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

decreases,  the  triple  valve  shifts  in  such  a  way  that  compressed  air 
passes  from  the  tank  E  into  the  cylinder  C;  this  compressed  air  drives 
the  piston  out  with  a  pressure  of  75  Ibs.  per  sq.  in.  and  puts  the 
brakes  "on." 

When  the  engineer  wishes  to  take  the  brakes  "off"  again,  he  turns  the 
lever  back.  This  closes  the  train  pipe  and  at  the  same  time  allows  air 
to  flow  from  tank  B  through  the  train  pipe  to  the  triple  valve  F.  When 
the  pressure  in  the  trian  pipe  increases,  the  triple  valve  shifts  back  in 
such  a  way  that  it  lets  air  pass  from  B  into  E,  also  it  closes  the  passage 
from  E  to  C,  and  lets  the  air  out  of  C.  The  spring  then  forces  the 
plunger  in  and  takes  the  brakes  "off". 

It  will  be  noticed  that  if  the  train  should  break  in  two  by  the  breaking 
of  a  coupling,  the  rubber  air  hose  connection  on  the  train  pipe  is  broken 
and  the  air  is  let  out  of  the  train  pipe.  This  automatically  sets  the 
brakes  on  each  car  and  both  parts  of  the  train  are  brought  to  a  standstill. 

You  will  now  make  and  operate  an  air  brake  and  illustrate  the 
working  of  the  cylinder,  triple  valve,  and  air  tank. 


EXPERIMENT  No.  60 

To  make  and  operate  an  air  brake  and  to  illustrate  the  working  of 
the  triple  valve,  cylinder,  air  tank,  and  train  pipe. 

Use  the  apparatus  as 
shown  in  Fig.  157,  open 
clip  1,  and  blow  air  into 
the  rubber  tube. 

Your  mouth  here  repre- 
sents the  compressor  and 
air  tank  on  the  locomo- 
tive, and  while  you  are 
blowing  air  into  the  tank 
E  you  are  representing 


Fig.     157. — Illustrating    the    Working    of    the 
Air  Brake 


the  conditions  when  the 
train  is  running  and  the 
brakes  are  "off".  You  will  notice  here  that  when  clip  1  is  open  and  2  is 
closed  the  triple  valve  is  admitting  air  to  the  tank  E,  the  cylinder  C  is 
open,  and  the  brakes  are  "off".  Clips  1  and  2  represent  the  triple  valve. 
Now  close  clip  1  and  open  clip  2.  Do  you  observe  that  the  compressed 
air  in  E  forces  the  piston  out?  This  is  exactly  what  happens  when  the 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING     123 


engineer  puts  the  brakes  "on".  You  will  notice  here  that  when  clip  1  is 
closed  and  2  is  opened,  the  triple  valve  has  closed  the  passage  between 
the  cylinder  and  train  pipe,  and  has  opened  the  pipe  between  E  and  the 
cylinder.  This  is  the  condition  when  the  brakes  are  "on". 

If  you  have  a  bicycle  pump,  use  it  instead  of  your  mouth  and  pump 
more  air  into  the  tank  E.  You  will  then  find  that  the  piston  is  driven 
out  with  greater  force. 

At  the  next  opportunity  examine  the  air  brakes  under  a  box  car  or 
flat  car  on  a  railway  siding.  Identify  the  air  tank,  cylinder,  piston  rod 
end,  the  triple  valve,  and  the  train  pipe.  Notice  that  the  outward  move- 
ment of  the  piston  rod,  moves  a  lever,  and  that  this  lever  in  turn  sets 
the  brakes. 

THE  FLAME  THROWER 

You  have  read  of  the  flame  throw- 
ers, which  were  used  during  the  war. 
You  will  illustrate  their  action  in  the 
next  experiment. 

A  flame  thrower  is  a  strong  metal 
tank  with  a  pipe  and  nozzle  leading 
from  the  bottom.  It  contains  a  mix- 
ture of  inflamable  oils  in  the  lower 


Fig.    158. — A    Flame-Thrower    in    Action 

part    and    above    this,    hydrogen    gas 
under  great  pressure. 

The  tank  is  carried  on  the  back  of 
the  soldier,  as  shown  in  Fig.  158,  and 
when  the  nozzle  is  opened  the  com- 
pressed hydrogen  drives  the  oil  out 
with  great  force.  The  oil  is  set  on 
fire  by  a  pilot  light  just  beneath  the 
nozzle  and  the  moving  stream  be- 
comes a  stream  of  flame  or  liquid 
fire. 


Fig.  159. — Showing  how  the  Compressed 

Hydrogen    drives    the    Oil   out   of   a 

Flame  Thrower 


124    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


EXPERIMENT  No.  61 

To  illustrate  the  action  of  the  flame  thrower. 

It  is  dangerous  to  illustrate  the  action  of  a  flame  thrower  with  oil 
and  you  will  use  water  instead. 

Arrange  the  apparatus  as  shown  in  Fig.  159.  To  load  the  flame 
thrower,  place  a  clip  on  the  rubber  tube,  put  a  stopper  and  elbow  on  the 
end,  insert  the  stopper  into  a  water  faucet,  open  the  faucet  gently,  open 
the  clip,  and  allow  water  to  enter  the  bottle  until  it  is  one  half  full, 
then  close  the  clip. 

The  flame  thrower  is  now  loaded;  the  water  represents  the  oil  and 
the  compressed  air  represents  the  compressed  hydrogen. 

Now  to  use  the  flame  thrower;  replace  the  elbow  and  stopper  at  the 
end  of  the  rubber  tube  by  a  nozzle,  turn  the  bottle  upside  down,  point 
the  nozzle  at  the  thing  you  wish  to  hit,  and  open  the  clip. 

THE  FIRE  EXTINGUISHER 

The  common  household  fire  ex- 
tinguisher, Fig.  160,  is  a  strong 
brass  cylinder  with  a  short  piece 
of  hose  attached  at  the  top;  this 
hose  and  its  nozzle  are  open  at 
all  times.  The  extinguisher  is 
charged  as  follows  :  In  the  bottom 
there  is  a  solution  of  \y2  Ibs.  of 
sodium  carbonate  (Na2CO3)  and  2l/2 
gal.  of  water,  and  above  this  there 
is  an  8  oz.  bottle  containing  4  ozs. 
of  strong  sulphuric  acid  (H2SOO. 
This  bottle  is  fitted  with  a  loose 
lead  stopper  which  falls  out  when 
the  extinguisher  is  turned  upside 
down. 

To    use    the    extinguisher,   you 
carry   it  right  side  up  to  the  fire, 
then  turn   it  upside  down  and  di- 
Fig.  160.— Showing  the  Outside  and        rect  the   stream  of  water  and  gas 
Inside  of  a  Fire  Extinguisher  upon    the    fire    by    means    of    the 

Courtesy  of  the  MacMillan  Co.  ghort   hose      Use   all   of   the   waterj 

because  once  you  have  turned  the  extinguisher  upside  down,  the  liquids 
are  mixed,  and  the  extinguisher  is  of  no  further  use  until  you  have  re- 


B*ca>  soumoi 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    125 


U" 


charged  it.  You  should  do  this  at  once  in  order  to  be  prepared  again 
for  a  fire.  In  recharging  you  should  follow  the  directions  printed  on  the 
case. 

The  action  which  takes  place  in  the  extinguisher  is  as  follows :  when 
you  turn  it  upside  down,  the  sulphuric  acid  and  sodium  carbonate  react 
chemically  and  produce  a  large  quantity  of  carbon  dioxide  gas.  The 
volume  of  carbon  dioxide  gas  produced  is  much  greater  than  the  volume 
of  the  cylinder  and  therefore  the  gas  exerts  pressure  on  the  water  and 
drives  it  out  with  great  force. 

The  fire  is  extinguished,  partly  by  the  water,  and  partly  by  the  gas. 
It  seems  strange  to  speak  of  putting  out  a  fire  by  means  of  gas,  but 
carbon  dioxide  gas  has  three  properties  which  make  it  very  valuable 
for  this  purpose:  first,  it  does  not  burn;  second,  it  does  not  support 
combustion,  that  is,  it  does  not  help  other  things  to  burn;  third,  it  is 
heavier  than  air.  The  carbon  dioxide  gas  surrounds 

/^x-57--^^  the  fire  and  smothers  it,  because  it  does  not  support 

fffft'  combustion  and  it  takes  the  place  of  the  air  which 

I'M  v,\ 

does  support  combustion. 


EXPERIMENT  No.  62 

To  make  and  operate  a  fire  extinguisher. 
You  will  not  use  strong  sulphuric  acid  because  it 
burns  practically  everything  it  touches,  but  instead 
you  will  use   a  dilute   acid,  vinegar;   also  you  will 
use  baking  soda  which  is  sodium  carbonate. 
Arrange  the  apparatus  as  shown  in  Fig.  161.    Pour 
six  tablespoonsful  of  vinegar  into 
the  bottle,  fill  the  bottle  four  fifths 
full  of  water  and  shake,  measure 
out  one  level  tablespoonful  of  bak- 
ing soda  and  place  it  on  a  piece 
of  paper  ready  for  use. 

Now  to  use  the  fire  extinguisher, 
go  outside  and  let  one  experi- 
menter hold  the  bottle  and  stopper 
while  the  other  holds  the  baking 
soda  and  the  nozzle.  Dump  the 
soda  into  the  bottle,  put  in  the 
stopper  quickly  and  hold  it  very 


Fig. 


161.— A    Home-Made    Fire-Ex 
tinguisher   in   Action 


126    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


firmly,  turn  the  bottle  upside  down  and  shake.    Does  the  gas  drive  the 
water  out  with  considerable  force? 

Repeat  the  experiment  but  this  time  make  a  cigarette  shaped  tissue 
paper  package  of  the  baking  soda  and  attach  the  open  end  to  the  under- 
side of  the  stopper  by  means  of  a  pin.  The  extinguisher  then  will  work 
when  you  turn  it  upside  down. 

Repeat  but  use  the  white  and  blue  packages  of  a  Seidlitz  powder 
instead  of  the  vinegar  and  soda.  Dissolve  the  contents  of  the  blue 
package  in  the  water  and  dump  in  the  contents  of  the  white.  They  pro- 
duce carbon  dioxide  gas. 

EXPERIMENT  No.  63 

To  show  how  carbon  dioxide  gas  puts  out  a  fire. 


Fig.  162.— Putting  Out  a  Match  and  a  Candle 
by  means  of  Heavy  Carbon  Dioxide  Gas 


POURING    CARBON  DIOXIDE  OAJ. 


You  can  show  that  the  carbon  dioxide  gas  (CO»)  is  heavy  and  that 
it  will  put  out  a  fire  as  follows :  Pour  six  tablespoonsful  of  vinegar  into 
an  empty  ten-quart  pail,  Fig.  162,  and  add  one  level  tablespoonful  of 
baking  soda.  Stir  with  a  spoon  until  the  fizzing  stops.  You  now  have 
the  bottom  of  the  pail  full  of  carbon  dioxide  gas.  You  cannot  see  it 
but  it  is  there.  Now  light  a  match  and  lower  it  slowly  into  the  pail. 

Does  it  go  out  when  it  gets  a  certain  distance  into  the  pail?  It 
goes  out  because  it  is  surrounded  by  carbon  dioxide  gas  which  does 
not  support  combustion. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    127 


Light  a  candle  and  lower  it  into  the  pail  in  the  same  way.  Does 
it  go  out?  It  goes  out  for  the  reason  stated  above. 

You  know  that  (CO2)  gas  is  heavier  than  air  because  it  remains  in 
the  bottom  of  the  pail.  If  it  were  lighter,  the  air  would  sink  to  the 
bottom  of  the  pail  and  lift  it  out. 

You  can  show  that  the  (CO2)  gas  is  heavy  and  that  it  will  pour  just 
like  water,  as  follows :  Put  a  lighted  match  or  a  very  short  lighted 
candle  at  the  bottom  of  an  empty  pail,  then  lift  the  pail  containing 
the  CO2  gas  and  pour  it  into  the  empty  pail  just  as  you  would  pour  water. 

Does  the  gas  put  out  the  match  or  candle?  This  shows  that  the  gas 
pours  and  therefore  that  it  is  heavier  than  air.  It  also  shows  again  that 
the  CO2  gas  puts  out  a  fire. 


THE  AIR  PUMP 


Fig.   163. — An  Air  Pump 
Courtesy  of  the  MacMillan  Co. 


The  air  pump  shown  here  has  a  solid 
plunger  and  two  valves  A  and  B ; 
valve  A  opens  inward  and  valve  B 
outward.  The  vessel  R,  out  of  which 
the  air  is  being  pumped,  has  an  open 
bottom  with  a  ground  edge  which  fits 
air-tight  on  the  smooth  greased  sur- 
face of  the  stand.  The  air  is  pumped 
out  through  a  hole  in  the  center  of 
the  stand  and  through  the  pipe  F. 

When  the  plunger  is  pulled  up,  valve 
B  closes  and  part  of  the  air  expands 


from  the  vessel  R  through  A  into  the  pump  cylinder  C.  When  the 
plunger  is  forced  down,  valve  A  closes  and  the  air  in  C  is  forced  out 
through  the  valve  B. 

When  the  plunger  is  again  raised  part  of  the  air  remaining  in  R 
expands  into  C  and  when  the  plunger  is  forced  down  this  air  is  forced 
out  through  B,  and  so  on. 

If  you  wish  to  pump  air  into  R  you  attach  it  to  B  instead  of  to  A 
and  operate  the  plunger.  Each  stroke  of  the  plunger  fills  the  cylinder 
C  with  air  and  each  down  stroke  forces  this  air  into  R. 


128    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


EXPERIMENT  No.  64 

To  make  and  operate  an  air  pump. 


Fig.  164. — Illustrating  the  Working  of 
an  Air  Pump 


Arrange  the  apparatus  as  in  (1)  Fig.  164  and  operate  the  plunger.  Do 
you  pump  air  out  of  the  bottle? 

Arrange  the  apparatus  as  in  (2)  Fig.  164  and  operate  the  plunger. 
Do  you  pump  air  into  the  bottle? 

THE  BICYCLE  PUMP  AND  TIRE 


Fig.  165.— The  Bicycle  Pump 
Courtesy  of  the  MacMillan  Co. 

The  bicycle  pump  is  a  very  simple  air  pump. 
It  consists  of  a  cylinder  C  and  a  plunger  P;  one 
valve  is  the  cup  shaped  piece  of  leather  on  the 
bottom  of  the  plunger,  and  the  other  is  the  valve 
S  which  remains  on  the  bicycle  tire,  T, 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    129 


When  the  plunger  is  moved  up  there  is  a  vacuum  left  in  the  space  C 
beneath,  and  the  pressure  of  the  atmosphere  forces  air  into  this  space 
around  the  sides  of  the  cup  valve  which  bends  in.  When  the  plunger  is 
forced  down,  the  air  in  C  is  forced  into  the  tire  through  the  valve  S, 
because  the  cup  leather  is  forced  outward  by  the  air  pressure  and  be- 
comes air-tight.  This  is  repeated  at  each  stroke. 

The  hand  pump,  at  the  right  has  a  hollow  plunger  stem  through  which 
the  air  passes  to  the  tire.  A  cup  leather  on  the  plunger  is  one  valve 
and  the  valve  on  the  tire,  the  other. 


2  3 

Fig.    166.—  The  Bicycle  Pump   in  Action 


EXPERIMENT  No.  65 

To  make  and  operate  two  bicycle  pumps. 

Arrange  the  apparatus  as  in  (1)  and  operate  the  plunger.  The  bottle 
with  its  valve  represents  the  bicycle  tire  with  its  valve.  Do  you  pump 
air  into  the  tire? 

Arrange  the  bottle  as  in  (2)  and  pump  air  into  it.  Does  the  com- 
pressed air  force  the  water  out? 

The  above  represents  the  action  of  a  large  bicycle  pump. 
Make   the   experiments    (3)    and    (4).    The   pump   here    represents   a 
hand  bicycle  pump. 
A  — 9 


130    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

THE  AIR  COMPRESSOR 

The  commercial  air  compres- 
sor is  simply  a  large  air  pump 
as  shown  in  Fig.  167.  It  has  a 
solid  plunger  P  and  two  valves. 
When  the  plunger  is  raised,  the 
pressure  of  the  atmosphere  lifts 
valve  Vi  and  forces  air  into  the 
pump  barrel;  when  the  plunger 
is  driven  down,  valve  Vi  closes 
but  valve  V2  opens  and  the  air  is  forced  into  the  storage  tank  R.  This 
operation  is  repeated  at  each  stroke.  The  pump  is  driven  by  a  steam 
engine,  gasoline  engine,  electric  motor,  or  water  wheel. 


Fig.    167. — Air    Compressor    Pump    and 

Storage  Tank 

From   the   "Ontario   High   School  Physics" 
By  Permission  of  the  Publishers 


THE  SAND  BLAST 

The  sand  blast,  one  form  of  which  is  illustrated 
in  (1)  Fig.  168,  is  used  to  clean  metal  castings, 
etch  glass,  cut  the  letters  in  marble,  clean  the  walls 
of  buildings,  and  so  on. 

The  sand  is  driven  by  compressed  air  with 
great  force  against  the  object  to  be  cleaned.  Each 
particle  of  sand  pulverizes  the  material  which  it 
strikes  and  since  millions  of  grains  strike  the 
material  each  minute,  the  surface  is  worn  away 
very  rapidly. 


Fig.     168. — Interior 
of  a   Sand   Blast. 
From  "Hitchcock's 
Compressed  A  ir  and 
Its  Apohcations1 ' 

Courtesy    of    the 

Norman    W.   Henley 

Publishing  Co. 


Fig.  168.— A  Sand  Blast 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    131 


The  inside  of  the  machine  is  represented  in  (2)  Fig.  168.  The  sand 
is  dumped  into  the  V  shaped  top  and  is  admitted  to  the  chamber  CC 
below  through  the  valve  A.  The  compressed  air  enters  at  B  and  passes 
out  to  the  hose  and  nozzle  through  the  tube  D.  The  sand  is  dropped 
into  the  moving  air  through  the  valve  F  and  is  carried  through  the  hose 
and  nozzle  to  the  object. 

EXPERIMENT  No.  66 

To  make  and  operate  a  sand  blast. 

Arrange  the  apparatus  as 
shown  in  Fig.  169.  The  sand 
is  held  in  the  funnel  and 
drops  down  into  the  moving 
air  when  the  clip  is  opened. 

Fill  the  funnel  with  dry, 
coarse  sand  and  ask  your 
partner  to  hold  his  hand 
over  the  funnel  and  open  the 
clip,  while  you  blow  air  into 
the  hose  and  hold  your  hand 

Fig.    169.— Illustrating  the  Working  of  * 

a  Sand  Blast  opposite  the  tee  opening  to 

feel  the  effect. 

Your  partner's  hand  must  be  held  over  the  funnel,  otherwise  part  of 
the  air  will  blow  up  through  the  sand. 

Repeat  this  with  the  bottle  used  as  a  compressed  air  tank.  Pump 
air  into  the  tank  by  means  of  a  bicycle  pump,  and  close  the  hose 
with  a  clip.  Connect  the  hose  with  the  tee,  ask  your  partner  to  hold 
his  hand  over  the  funnel  and  open  the  funnel  clip,  then  hold  your  hand 
in  front  of  the  tee  opening,  and  open  the  clip  on  the  hose. 

Do  you  find  that  the  sand  strikes  your  hand  with  considerable  force? 

PNEUMATIC  PAINT  BRUSH 

The  working  of  the  pneumatic  paint  brush  is  as  follows :  The  com- 
pressed air  enters  through  the  hose  and  handle  and  issues  from  a  small 
nozzle.  The  current  of  air  thus  produced  carries  out  with  it  the  air 
around  the  nozzle  and  creates  a  partial  vacuum.  The  atmospheric  pres- 
sure on  the  paint  in  the  tank  then  forces  paint  into  the  vacuum  around 
the  nozzle,  and  this  paint  is  carried  out  through  the  large  nozzle  by  the 
air  current.  The  air  pressure  is  from  50  to  80  tbs.  per  sq.  in.  and  the 
stream  of  paint  can  be  regulated  from  a  fine  mist  to  a  solid  stream. 


132    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.  170.— A  Pneumatic  Paint  Brush 


Paint    Nozzle 

From  "Hitchcock's  Compressed 
Air  and  Its  Applications" 

Courtesy    of  the 
Norman  W.  Henley  Publishing  Co. 


This  form  of  paint  brush  is  used  in  all  kinds  of  painting  and  per-- 
mits  very  rapid  work.  It  is  used  in  painting  buildings,  bridges,  machin- 
ery, railway  cars,  furniture  and  even  pictures,  also  in  calsomining  and 
white-washing  walls,  houses  and  fences,  and  in  spraying  disinfectants 
in  hospitals,  camps,  trenches,  hen  houses,  etc.  The  common  atomizer  is 
made  on  the  same  principle. 

EXPERIMENT  No.  67 

To  make  and  operate  a  pneumatic  paint  brush. 

Arrange  the  apparatus  as  in  Fig.  171  and  blow  hard  into  the  rubber 
tube. 

Do  you  observe  that  water  rises  from  the  tumbler  into  the  wide  tube, 
and  issues  from  the  narrow  tube  in  the  form  of  a  light  spray? 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING     133 


Fig.    171. — Showing    how 
the    Pneumatic    Paint 
Brush  works 


This  is  very  interesting, 
because  it  shows  that  al- 
though you  blow  air  into 
the  wide  tube  you  create 
a  partial  vacuum  in  the 
tube.  The  reason  for  this 
is  as  follows :  The  com- 
pressed air  from  the  noz- 
zle enters  the  narrow  tube  with  great  velocity  and  in  doing  so  carries 
air  from  the  wide  tube  along  with  it.  This  creates  a  partial  vacuum 
in  the  wide  tube  and  the  pressure  of  the  atmosphere  lifts  water  from  the 
tumbler  into  the  wide  tube.  The  water  is  then  carried  into  the  narrow 
tube  by  the  stream  of  compressed  air  and  issues  from  the  end. 


THE  DIVING  BELL 

The  diving  bell,  Fig.  172,  is  simply  a  large 
iron  bell  open  at  the  bottom.  It  is  used 
to  enable  men  to  work  on  the  bottom  of  a 
river,  lake,  or  ocean,  for  example,  to  lay 
the  foundations  of  bridges,  wharves,  light- 
houses, etc. 

The  bell  is  made  large  enough  to  hold  a  , AIR  PUMPS 
number  of  men,  heavy  enough  to  sink  read- 
ily in  the  water,  and  strong  enough  to  stand 
the  great  pressure  of  the  water  on  the  out- 
side. It  is  usually  carried  in  a  ship  in  a  AIR  BUBBLE 
special  compartment  called  a  well :  this  is 
simply  a  hole  in  the  bottom  of  the  ship, 
lined  up  on  all  sides  to  prevent  water  from 
entering  the  ship.  The  bell  is  raised  and 
lowered  by  means  of  a  winch  and  pulleys, 
and  is  supplied  with  compressed  air  through 
a  strong  rubber  tube  attached  to  an  air 
pump  on  the  ship. 


Fig.   172.     A  Diving  Bell  used 

to    Work    under    Water 
Courtesy  of  the  MacMillan  Co. 


When  it  is  desired  to  use  the  diving  bell,  the  sailors  first  anchor 
the  ship  fore  and  aft  over  the  spot  where  the  work  is  to  be  done,  then 
the  workmen  get  into  the  bell  through  the  bottom,  the  air  pump  is 
started,  and  the  bell  is  lowered  by  means  of  the  winch  and  pulleys. 


134    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.    173. — A  Large  Diving  Bell  used 
as  an  Undersea  Storehouse  by  Divers 
Courtesy  of  the  Scientific  A  merican 


The  compressed  air  which  is  forced 
into  the  bell  supplies  the  men  with 
fresh  air  and  also  prevents  the 
water  from  entering  the  bottom  of 
the  bell;  the  excess  air  escapes  in 
bubbles  under  the  edge  of  the  bell. 
A  form  of  diving  bell  used  by 
divers  is  illustrated  in  Fig.  173.  It 
is  lowered  by  a  heavy  cable  from  a 
ship  at  the  surface,  from  which  it 
is  supplied  with  compressed  air, 
electricity,  and  telephone  connec- 
tion. The  diver  carries  his  air  in 
a  tank  on  his  back  and  is  there- 
fore not  encumbered  by  a  heavy 
air  hose;  the  light  cable  which  he 
drags  is  his  telephone  connection. 
The  bell  serves  as  a  store  house  for 
tools  and  as  a  place  to  which  the 
diver  can  retreat  to  repair  his  suit 
if  necessary.  He  enters  and  leaves 
the  bell  through  an  opening  near 
the  bottom  as  shown. 


EXPERIMENT  No.  68 

To  make  and  operate  a  diving  bell. 

Place  a  piece  of  a  match  stick  on  the  surface  of  the  water  in  a  wash 
bowl.  Invert  an  empty  tumbler  over  the  match  and  force  the  tumbler  to 
the  bottom  of  the  bowl  without  letting  air  escape.  Do  you  notice  that 
the  water  enters  the  tumbler  only  to  a  very  sligh  extent  and  that  you 
can  make  the  match  rest  on  the  bottom  of  the  bowl. 

The  tumbler  represents  the  diving  bell  and  the  match  stick  represents 
the  man,  who  could  now  go  to  work  on  the  bottom  of  the  river  or  lake. 
Of  course,  the  man  in  a  regular  diving  bell  would  not  get  into  the  water 
first  but  would  stand  or  sit  on  a  shelf  inside  the  bell.  Raise  the  tumbler 
gradually  and  notice  that  the  water  lifts  the  match  up  again. 

In  this  experiment  the  lower  edge  of  the  diving  bell,  the  tumbler,  is 
only  six  or  eight  inches  under  the  surface  of  the  water,  therefore  the 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    135 


Fig.    174. — Illustrating    the    Working    of 
the  Diving  Bell 

pressure  of  the  water  upward  on 

the    air    in    the   bell   is    small,    and 

the  air  is  only  slightly  compressed. 

When    the    regular    diving   bell    is 

sunk  in  water,  however,  the  pres- 
sure of  the  water  upward  on  the 

air  in  the  bell  increases  as  the  bell 
5  sinks   deeper  and  deeper  and  the 

water  would  rise  in  the  bell,  were  it  not  that  the  compressed  air  is 
pumped  in  at  sufficient  pressure  to  overcome  this  water  pressure  and 
to  keep  the  water  out. 

Repeat  the  experiment  with  the  hose  as  in  (2).  Open  the  hose.  Is 
the  air  forced  out?  Blow  air  into  the  hose.  Is  the  water  forced  out? 

Lift  a  boat  above  the  water  level  as  in  (3),  (4)  and  (5).  Make  the 
experiment  with  the  metal  tank  used  as  the  diving  bell  (6). 

EXPERIMENT  No.  69 

To  make  a  home-made  diving  bell. 

You  can  have  fun  in  your  swimming  pool  by  using  either  a  12  qt. 
pail,  a  wash  boiler,  or  a  wash  tub,  as  a  diving  bell.  Do  this  as  follows : 

Place  the  inverted  pail  over  your  head  and  let  yourself  sink.  You 
will  find  that  you  can  breath  under  the  pail  for  a  short  time  but  that  the 


136    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

air  soon  needs  renewing.  You  will  find  also  that  you  cannot  sink  very 
far,  because  the  buoyancy  of  the  inverted  pail  is  greater  than  the  weight 
of  your  body  in  water. 

Repeat  the  experiment  with  a  wash  boiler 
or  wash  tub.  You  will  find  again  that  you 
can  breath  under  the  boiler  or  tub.  You  will 
find  also  that  you  cannot  sink  the  boiler 
or  tub  because  their  buoyancy,  when  inver- 
ted and  filled  with  air,  is  much  greater  than 
the  weight  of  your  body  in  water. 

Make  this  experiment.  Go  to  a  part  of 
the  swimming  pool  where  you  can  sit  on 
the  bottom  with  your  head  above  water. 

then  let  tw°  °*  VOur  friends  Place  the  tub» 
upside  down  and  full  of  air,  over  your  head 

and  force  it  down  gently  until  the  bottom 

of  the  tub  is  slightly  under  the  surface.  Your  head  is  now  below  the 
level  of  the  water  outside,  but  you  will  find  that  you  have  plenty  of  air 
in  the  tub  because  the  water  level  in  the  tub  is  only  slightly  above  the 
level  of  the  edge  of  the  tub. 

Make  experiments  of  your  own. 


PNEUMATIC  CAISSONS 

A  caisson  similar  to  that  shown  here  is  used  to  remove  the  earth 
down  to  the  rock  for  the  foundations  of  bridge  piers.  It  is  filled  with 
compressed  air  which  drives  the  water  out  at  the  bottom  and  leaves 
the  earth  dry  for  the  workmen. 

The  caisson  is  closed  in  on  all  sides  to  keep  out  the  water.  It  is 
open  at  the  bottom  but  is  closed  above  by  well  braced  timbers  weighted 
down  by  concrete  C.D.  The  bottom  is  let  down  into  the  mud,  the  com- 
pressed air  is  turned  on  to  force  the  water  out  of  the  working  chamber, 
and  the  workmen  then  enter  the  working  chamber  to  excavate  the  mud. 
The  weight  of  the  concrete  CD.  gradually  sinks  the  caisson,  as  the  mud 
is  excavated,  until  the  solid  rock  is  reached. 

The  men  enter  the  caisson  through  the  air  lock  L,  as  follows :  The 
lower  door  B  is  closed,  compressed  air  is  let  out  of  L,  the  door  A  is 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    137 


opened,  the  workmen  enter,  the  door  A  is 
closed  and  compressed  air  is  admitted  slow- 
ly to  L  until  its  pressure  is  equal  to  that 
below;  the  door  B  is  then  opened  and  the 
men  climb  down  a  ladder  into  the  caisson. 
The  men  leave,  and  ttiud  is  lifted  out 
through  the  air-lock  by  the  reverse  pro- 
ceedure. 

When  the  caisson  is  down  to  the  rock, 
the  working  chamber  and  the  space  above 
are  filled  with  concrete  to  serve  as  the  foun- 
dation of  the  bridge.  Sometimes  the  outer 
casing  of  the  caisson  is  removed,  but  more 
often  it  is  left  where  it  is. 

EXPERIMENT  No.  70 

To  make  and  operate  a  pneumatic  caisson 


-Section  of  a  Pneumatic  Caisson.  The  sides  of  tho 
caisson  are  extended  upward  and  are  strongly  braced  to  keep 
back  the  water  Masonry  or  concrete,  C.  D,  placed  on  top  el 
the  caisson,  press  it  down  upon  the  bottom,  while  compressed 
air.  forced  through  a  pipe  />,  drives  the  water  out  of  tho 
working  chamber.  To  leave  the  caisson  the  workman  climb* 
up  and  pauses  through  the  open  door  B  Into  the  air-lock  L. 
The  door  B  is  tben  closed  and  the  air  u  allowed  to  escape- 
from  L  until  it  is  at  atmospheric-  pressure.  Then  door  A 
to  opened.  In  order  to  enter,  this  process  it  reversed. 
Material  i»  hoisted  out  in  the  same  way  or  ii  sucked  out 


Fig.  176 

From  the  "Ontario  High 
and  to   show  how  a  man   enters   it   through    School  Physics",  By  Permission 

the  air-lock.  of  the  Publishers 

Arrange  the  apparatus  as  shown  in  Fig.  177.  The 
wide  tube  represents  the  caisson  and  the  narrow  tube 
at  the  top,  the  air-lock;  the  clips  represent  the  upper 
and  lower  doors  of  the  air-lock. 

Put  the  caisson,  with  both  clips  open,  in  the  sealer 
full  of  water. 

Do  you  find  that  the  water  level  inside  the  caisson 
is  the  same  as  that  outside? 

Now  blow  air  in  through  the  air  lock  and  close  one 
or  both  clips. 

Do  you  find  that  the  water  level  inside  the  caisson 
is  now  at  the  bottom? 

This  illustrates  the  manner  in  which  compressed  air 
forces  the  water  out  at  the  bottom  of  a  real  caisson. 

Now  to  show  how  a  man  enters  the  caisson  without 
Fig.    177.— Illus-    letting  out  the  compressed  air,  proceed  as  follows  : 
trating  the  Working         __  .  ,  A,     ,    ,     ,. 

of  a  Pneumatic  ^se  a  pm  to  represent  the  man,  be  sure  that  both 

Caisson  doors  are  closed,  then  open  the  upper  door  and  drop 

the  pin  into  the  air-lock  head  downwards,  not  that  the 


138    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 

man  enters  head  downwards,  but  the  head  of  the  pin  will  not  stick  into 
the  rubber  as  the  point  might. 

Now  open  the  lower  door. 

Does  the  pin  drop  to  the  bottom  and  has  the  whole  operation  been 
completed  without  letting  air  out  of  the  caisson  or  water  into  it. 

This  represents  the  way  a  man  would  enter  the  caisson.  It  is  called 
"locking  in".  The  man  of  course  would  not  drop  from  the  air  lock  to 
the  bottom  of  the  caisson;  he  would  climb  down  a  ladder.  Tools  and 
materials  are  admitted  to  the  caisson  in  the  same  way,  and  removed  by 
reverse  operation. 

EXPERIMENT  No.  71 

To  show  how  a  torpedo  is  shot  out  of  a  submarine  or  battle  ship. 


Fig.    178. — The   Revolver  Torpedo   Tube   in   Submarines 

By  carrying  the  torpedoes  in  a  revolving  cradle  back  of  the  torpedo  tube,  it  is  possible 
to  fire  several  torpedoes  in  rapid  succession  while  the  submarine  is  bearing  on  the  enemy 

A  torpedo  is  fired  out  of  a  submarine  or  battle  ship  by  means  of 
compressed  air  and  is  kept  in  motion  after  it  is  fired  by  means  of 
a  compressed  air  motor. 

Show  how  the  torpedo  is  fired,  by  means  of  the  apparatus  Fig.  179. 
The  bottle  here  represents  the  compressed  air  tanks  on  the  battleship, 
the  wide  tube  represents  the  torpedo  tube  and  the  plunger,  the  torpedo. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    139 


1  2 

Fig.    179. — Showing    How   a    Ship    is    Torpedoed 


Close  the  bottle  by  means  of  cord  and  rubber  bands  and  compress 
air  in  it  by  means  of  a  bicycle  pump  (1)  if  you  have  one ;  if  not,  attach 
the  rubber  tube  to  a  water  faucet  by  means  of  an  elbow  and  stopper 

(2)  and  fill  the  bottle  half  full  of  water  in  order  to  compress  the  air 
to  half  its  first  volume  and  thereby  give  it  a  pressure  of  15  ft>s.  per  sq.  in. 
Connect  the  bottle  with  the  torpedo  tube,  point  the  tube  at  the  ship 

(3)  and   open   the   clip.    Do  you   torpedo   the   ship   in   a  very   realistic 
manner 

EXPERIMENT  No.  72 

To  show  how  the  men  in  a  submarine  could  be  supplied  with  air 
taken  from  sea  water. 

Arrange  the  apparatus  as  in  (1)  Fig.  180.  The  space  between  the 
stoppers  is  completely  filled  with  water  and  is  free  from  air;  the  plunger 
is  covered  with  water  to  make  it  air-tight. 


140    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


Fig.    180. — Showing    How    a    Submerged    Submarine    could    take 
Air   from    Sea    Water 

Now  lift  the  plunger  as  in  (2).  Do  you  observe  that  air  bubbles  come 
out  of  the  water?  Let  the  plunger  go  back  (3).  Do  you  observe  that 
there  is  a  small  bubble  of  air  between  the  rubber  stoppers?  This  is 
extremely  interesting  and  is  explained  as  follows :  All  water  on  the 
earth  which  is  exposed  to  the  air  has  air  dissolved  in  it,  (the  fish  in 
water  live  on  this  air).  When  you  lift  the  plunger  you  produce  a 
vacuum  above  the  water  and  thereby  reduce  the  pressure  on  the  water 
•to  zero.  The  air  in  the  water  then  expands  into  bubbles  and  escapes 
from  the  water. 

Submarines  could  be  supplied  with  pure  air  when  under  water  as 
follows :  They  would  need  a  pump  similar  to  your  apparatus  above  but 
arranged  as  follows  :  During  the  upstroke  of  the  plunger  the  inlet  valve 
would  open  for  say  only  54  of  the  stroke  and  then  close  for  the  re- 
maining 24  °f  tne  stroke.  The  plunger  would  thus  draw  in  water  during 
]/4  stroke,  and  would  produce  a  vacuum  above  the  water  for  the  remain- 
ing $4  stroke,  the  air  in  the  water  would  then  expand  and  escape  from 
the  water. 

On  the  down  stroke  of  the  plunger  the  air  and  water  would  be  forced 
out  of  the  pump  but  on  their  way  out  of  the  submarine  they  would  pass 
through  a  tank,  the  air  would  escape  into  the  tank  but  the  water  would 
pass  on  out.  The  air  accumulated  in  the  tank  could  then  be  used  in 
the  submarine. 


FINIS 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    141 


TABLE  OF  CONTENTS 


HYDRAULIC  ENGINEERING 

WATER  SUPPLY. 

Experiment 

1.  To  make  and  operate  a  city  water  supply  system  in  which  the  water  comes 
from  a  standpipe,  reservoir,  or  lake. 

2.  To  make  and  operate  a  private  water  supply  system  in  which  the  water  is 
stored  in  a  tank  on  a  tower. 

3.  To  make  and  operate  a  private  water  supply  system  in  which  the  water  is 
stored  in  an  attic  tank. 

4.  To  show  how  water  is  brought  from  an  elevated  well  or  spring. 
Game       1.     A  Naval  Battle. 

PNEUMATIC  TANK  SYSTEM  OF  WATER  SUPPLY. 

Experiment 

5.  To  make  and  operate  a  pneumatic  tank. 
Game      2.     Rapid  Fire  Water  Gun. 
Experiment 

6.  To  make  and  operate  a  pneumatic  tank  system  of  water  supply. 

WATER  AND  AIR. 

7.  To  show  that  water  is  incompressible  and  that  air  is  compressible. 

8.  To  show  that  compressed  air  exerts  pressure. 
Game       3.     Trench  Gun. 

4.  Height  and  Distance  Contest 

5.  Pop  Gun. 

THE  SIPHON. 

Experiment 

9.  To  make  and  operate  a  siphon. 

HOW  THE  SIPHON  IS  USED  IN  WATER  SUPPLY  SYSTEMS. 

10.  To  show  how  the  siphon  is  used  in  water  supply  systems. 
HOW  TO  START  A  LARGE  SIPHON. 

11.  To  illustrate  different  methods  of  starting  a  large  siphon. 
OTHER  USES  OP  THE  SIPHON. 

12.  To  illustrate  other  uses  of  the  siphon. 
VELOCITY  OF  FLOW. 

13.  To  show  that  the  velocity  of  the  water  in  a  siphon  is   greater  the  greater 
the  vertical  distance  between  the  water  levels  about  the  two  arms. 
OTHER  SIPHONS. 

14.  To  make  and  operate  a  double  siphon  and  a  three-legged  siphon. 
HOW  TO  START  A  SMALL  SIPHON. 

15.  To  illustrate  two  ways  of  starting  a  small  siphon. 
AN  INCLOSED  FOUNTAIN. 

16.  To  make  and  operate  an  inclosed  fountain. 


142    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


ATMOSPHERIC  PRESSURE. 

AIR  HAS  WEIGHT.  AIR  EXERTS  PRESSURE. 

Experiment 

17.  To  show  that  the  atmosphere  exerts  pressure. 

18.  To  show  that  the  atmosphere  will  support  a  column  of  water. 

19.  To  prove  that  it  is  the  pressure  of  the  atmosphere  which  lifts  the  water. 

20.  To  show  in  other  ways  that  the  atmosphere  exerts  pressure  downward  and 
upward. 

21.  To  illustrate  two  simple  uses  of  atmospheric  pressure 

THE  "WHY"  OF  THE  SIPHON, 

PUMPS. 

22.  To  illustrate  the  action  of  a  syringe. 
Game      6.     Water  Gun  Shooting. 

7.  Big  Gun  Battle. 

8.  Machine  Gun  Battle. 

9.  The  Diablo  Whistle. 
Experiment 

THE  LIFT  PUMP. 

23.  To  make  and  operate  a  lift  pump. 
THE  FORCE  PUMP. 

24.  To  make  and  operate  a  force  pump. 

25.  To  show  how  water  is  pumped  into  an  elevated  tank. 
Game    10.     Force  Pump  Contest. 

HYDRAULIC  APPLIANCES. 

PASCAL'S  LAW. 

Experiment 

*  26.     To    show    that    pressure    exerted    on    water    is    transmitted    equally    in    all 

directions. 

27.  To  make  and  operate  a  hydrostatic  bellows. 
THE  HYDRAULIC  PRESS. 

28.  To  make  and  operate  a  hydraulic  press. 
THE  HYDRAULIC  ELEVATOR. 

29.  To  make  and  operate  a  hydraulic  elevator. 

HYDRAULIC  LIFT  — LOCKS. 

CANAL  LOCKS.          LIFT  LOCKS. 

30.  To  make  and  operate  a  hydraulic  lift-lock. 
THE  PRESSURE  EXERTED  BY  WATER. 

31.  To  show  that  the  pressure  at  a  nozzle  is  independent  of  the  size  and  shape 
of  the  tank  and  pipe. 

THE  HYDROSTATIC  PARADOX. 

32.  To  illustrate  the  hydrostatic  paradox. 

EXPLANATION  OF  HYDROSTATIC  PARADOX. 

HOW  TO  CALCULATE  THE  PRESSURE  EXERTED  BY  WATER. 


HYDRAULIC  AND  PNEUMATIC  ENGINEERING    143 

PRESSURE  UNDER  WATER. 

THE  DEPTH  BOMB,  TORPEDO  AND  SUBMARINE. 

Experiment 

33.  To   show  that  the  pressure  under  water   increases    with   the  depth  and  that 
it  is  equal  in  all  directions  at  any  depth. 

34.  To  show  that  water  exerts  pressure  upward  on  anything  under  its  surface 
and   that   this   upward    pressure   is    equal   to   the   downward   pressure  at  any 
depth. 

HOW  TO  CALCULATE  THE  PRESSURE  ON  DEPTH  BOMB, 
TORPEDO,  AND  SUBMARINE. 

BUOYANCY 

WHY  DOES  A  STEEL  SHIP  FLOAT? 

Experiment 

35.  To  illustrate  the  buoyant  effect  ot  water. 
THE  LAW  OF  ARCHIMEDES. 

36.  To  illustrate  the  law  of  Archimedes. 

37.  To  illustrate  the  law  of  Archimedes  for  bodies  which  sink  in  -water. 
RAISING  SUNKEN  SHIPS. 

38.  To  show  how  sunken  ships  are  raised  by  means  of  air. 
FLOATING  DRY  DOCK. 

39.  To  make  and  operate  a  floating  dry-dock. 
THE  SMALL  SUBMARINE. 

40.  To  make  the  small  submarine  submerge  and  rise  in  water. 

RUNNING  WATER. 

FRICTION. 

41.  To  illustrate  the  effect  of  friction  on  running  water. 
NOZZLES. 

42.  To  show  why  the  stream  is  longer  with  a  nozzle  than  without. 
Experiment 

43.  To  show  that  you  put  less  water  on  a  road  in  a  given  time  with  a  nozzle 
than  without. 

VELOCITY  OF  FLOW. 

44.  To   show   that   the   velocity    of   water    is    doubled    when   the   head   is   made 
four  times  as  great. 

AIR  LOCK. 

45.  To  illustrate  an  air  lock. 

PNEUMATIC  ENGINEERING 

ATMOSPHERIC  PRESSURE. 

Experiment 

46.  To  show  that  the  atmosphere  exerts  pressure. 

HOW  ATMOSPHERIC  PRESSURE  WAS  FIRST  MEASURED. 

47.  To  measure  the  pressure  of  the  atmosphere. 
THE  BAROMETER. 

HOW  AIRMEN  KNOW  THEIR  ALTITUDE. 
THE  ALTITUDE  GAUGE. 


144    HYDRAULIC  AND  PNEUMATIC  ENGINEERING 


THE  WATER  BAROMETER. 

48.  To   show  that   the  vertical   height  to  which   the   atmosphere  will  lift  water 
is  independent  of  the  length  and  slant  of  the  tube. 

49.  To  show  that  the   height  to   which   the   atmosphere   will   lift   water   is   inde- 
pendent of  the  size  and  shape  of  the  tube  and  of  the  water  surface  outside 
the  tube. 

50.  To  show  that  the   atmosphere  lifts  heavy   salt   water  to   a  less  height,   and 
light  gasoline  to  a  greater  height,  than  it  lifts  fresh  water. 

51.  To  show  that  the  atmosphere  will  lift  weights. 

52.  To  show  that  the  atmosphere  will  lift  15  Ibs.  per  square  inch  but  no  more. 
AIR-LIFT  PUMPS. 

53.  To  make  and  operate  two  air-lift  pumps. 
LAWS  WHICH  APPLY  TO  GASES. 
PASCAL'S  LAW. 

54.  To  illustrate  Pascal's  law  as   it  applies  to  gases. 

BALLOONS  AND  THE  BUOYANT  FORCE  OF  AIR. 
THE  LAW  OF  ARCHIMEDES  APPLIED  TO  AIR. 
HOW  THE  TOTAL  LIFT  OF  A  BALLOON  IS  CALCULATED. 
Experiment 

55.  To  illustrate  the  buoyant  force  of  air. 

56.  To    illustrate   the   buoyant   force  of   air   by    means    of   a    balloon    filled    with 
hydrogen. 

57.  To  shoot  down  a  balloon. 

58.  To   illustrate   the   buoyant   force   of   a   gas   heavier  ,than   air   by   means   of  a 
soap  bubble  filled  with  air. 

COMPRESSED  AND  EXPANDED  GASES. 

BOYLE'S  LAW. 

59.  To  illustrate  Boyle's  law. 
THE  AIR  BRAKE. 

60.  To   make   and    operate   an   air  brake   and    to    illustrate   the    working    of   the 
triple  valve,  cylinder,  air  tank,  and  train  pipe. 

THE  FLAME  THROWER. 

61.  To  illustrate  the  action  of  the  flame  thrower. 
THE  FIRE  EXTINGUISHER. 

62.  To  make  and  operate  a  fire  extinguisher. 

63.  To  show  how  carbon  dioxide  gas  puts  out  a  fire. 
THE  AIR  PUMP. 

64.  To  make  and  operate  an  air  pump. 
THE  BICYCLE  PUMP  AND  TIRE. 

65.  To  make  and  operate  a  bicycle  pump. 
THE  AIR  COMPRESSOR. 

THE  SAND  BLAST. 

66.  To  make  and  operate  a  sand  blast. 
PNEUMATIC  PAINT  BRUSH. 

67.  To  make  and  operate  a  pneumatic  paint  brush. 
THE  DIVING  BELL. 

Experiment 

68.  To  make  and  operate  a  diving  bell. 

69.  To  make  a  home-made  diving  bell. 

PNEUMATIC  CAISSONS. 

70.  To  make  and   operate  a   pneumatic   caisson   and  to  show  how  men  enter   it 
through  the  air-lock. 

71.  To  show  how  a  torpedo  is  shot  out  of  a  submarine  or  battle  ship. 

72.  To   show  how   the   men   in    a   submarine   could   be   supplied   with   air   taken 
from  sea  water, 


MEMORANDUM 


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WATER 
AND   AIR 

Two  very  common  yet 
important  substances  and 
very  powerful  too  when 
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comes  out  of  a  faucet 
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THE  A.  C.  GILBERT  COMPANY 
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I 


Can  You  Lay 

Out  a 
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BOY  ENGINEERING 


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505  Blatchley  Avenue 
New  Haven    :    Conn. 


24152 


88971 7 


C^X^yV   , 

THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


